{"id":2541,"date":"2016-10-18T23:39:01","date_gmt":"2016-10-18T23:39:01","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=2541"},"modified":"2024-09-02T14:41:50","modified_gmt":"2024-09-02T14:41:50","slug":"aplicacoes-das-leis-de-newton","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/raciocinio-logico\/aplicacoes-das-leis-de-newton\/","title":{"rendered":"Aplica\u00e7\u00f5es das leis de newton"},"content":{"rendered":"

APLICA\u00c7\u00d5ES DAS LEIS DE NEWTON<\/b><\/span><\/span><\/span><\/p>\n

A teoria para esses exerc\u00edcios encontra-se em <\/b><\/span><\/span><\/span>fisicaevestibular.com.br<\/b><\/span><\/span><\/span> – <\/b><\/span><\/span><\/span>Mec\u00e2nica – <\/b><\/span><\/span><\/span>nos setores: <\/b><\/span><\/span><\/span>Primeira Lei de Newton, Segunda Lei de Newton, Terceira Lei de Newton, Tipos de For\u00e7as, Peso e Massa, Polias e Roldanas, Aplica\u00e7\u00f5es das Leis de Newton para corpos apoiados ou suspensos e For\u00e7as no Movimento Circular.<\/b><\/span><\/span><\/span><\/p>\n

Exerc\u00edcios de vestibulares com resolu\u00e7\u00f5es comentadas sobre <\/b><\/span><\/span><\/span><\/p>\n

Aplica\u00e7\u00f5es das leis de Newton<\/b><\/span><\/span><\/span><\/p>\n

01-(UNIFESP-SP)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Suponha que um comerciante inescrupuloso aumente o valor assinalado <\/b><\/span><\/span><\/span>pela sua <\/b><\/span><\/span><\/span>balan\u00e7a, empurrando sorrateiramente o prato para baixo com uma for\u00e7a de m\u00f3dulo F = 5,0 N, <\/b><\/span><\/span><\/span>na <\/b><\/span><\/span><\/span>dire\u00e7\u00e3o e sentido indicados <\/b><\/span><\/span><\/span>na figura.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Com essa <\/b><\/span><\/span><\/span>pr\u00e1tica, ele consegue fazer<\/b><\/span><\/span><\/span> com que uma <\/b><\/span><\/span><\/span>mercadoria de massa 1,5 kg<\/b><\/span><\/span><\/span> seja <\/b><\/span><\/span><\/span>medida<\/b><\/span><\/span><\/span> por essa <\/b><\/span><\/span><\/span>balan\u00e7a como se tivesse massa de:<\/b><\/span><\/span><\/span> considere <\/b><\/span><\/span><\/span>g = 10 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0e sen37<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sup><\/span>= 0,6<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span><\/span>3,0 kg.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span><\/span>2,4 kg.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/span> <\/b><\/p>\n

c) <\/b><\/span><\/span><\/span><\/span>2,1 kg.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span><\/span>1,8 kg.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>1,7 kg.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

02-(UFPE-PE)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>bloco A, <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>massa<\/b><\/span><\/span><\/span> igual a <\/b><\/span><\/span><\/span>2,0 kg, <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>colocado sobre um bloco B, <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>massa <\/b><\/span><\/span><\/span>igual <\/b><\/span><\/span><\/span>4,0 kg, <\/b><\/span><\/span><\/span>como mostrado <\/b><\/span><\/span><\/span>na figura.<\/b><\/span><\/span><\/span><\/p>\n

Sabendo-se <\/b><\/span><\/span><\/span>que o <\/b><\/span><\/span><\/span>sistema permanece em repouso <\/b><\/span><\/span><\/span>sobre uma <\/b><\/span><\/span><\/span>mesa, <\/b><\/span><\/span><\/span>calcule a <\/b><\/span><\/span><\/span>for\u00e7a que a mesa exerce sobre o bloco B, em newtons.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

03-(UFSCAR-SP)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>jo\u00e3o-teimoso <\/b><\/span><\/span><\/span>\u00e9 um <\/b><\/span><\/span><\/span>boneco<\/b><\/span><\/span><\/span> que, <\/b><\/span><\/span><\/span>deslocado de sua posi\u00e7\u00e3o de equil\u00edbrio, <\/b><\/span><\/span><\/span>sempre <\/b><\/span><\/span><\/span>volta a ficar em p\u00e9. <\/b><\/span><\/span><\/span>Suponha que <\/b><\/span><\/span><\/span>uma crian\u00e7a segure um jo\u00e3o-teimoso <\/b><\/span><\/span><\/span>na <\/b><\/span><\/span><\/span>posi\u00e7\u00e3o <\/b><\/span><\/span><\/span>da figura e <\/b><\/span><\/span><\/span>logo <\/b><\/span><\/span><\/span>em <\/b><\/span><\/span><\/span>seguida o solte, sobre<\/b><\/span><\/span><\/span> uma <\/b><\/span><\/span><\/span>superf\u00edcie horizontal.<\/b><\/span><\/span><\/span><\/p>\n

Assinale a alternativa <\/b><\/span><\/span><\/span>que <\/b><\/span><\/span><\/span>melhor representa o esquema das for\u00e7as <\/b><\/span><\/span><\/span>que, com <\/b><\/span><\/span><\/span>exce\u00e7\u00e3o das for\u00e7as de atrito, atuam sobre o jo\u00e3o-teimoso deitado, imediatamente <\/b><\/span><\/span><\/span>ap\u00f3s ser <\/b><\/span><\/span><\/span>solto pela crian\u00e7a.<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0<\/span><\/p>\n

04-(UFRJ-RJ)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Uma <\/b><\/span><\/span><\/span>pessoa idosa, de 68kg, pesa-se <\/b><\/span><\/span><\/span>com <\/b><\/span><\/span><\/span>sua bengala apoiada no ch\u00e3o, <\/b><\/span><\/span><\/span>ao <\/b><\/span><\/span><\/span>lado da balan\u00e7a<\/b><\/span><\/span><\/span>, como mostra a <\/b><\/span><\/span><\/span>figura. \u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

Com a <\/b><\/span><\/span><\/span>pessoa em repouso a leitura da balan\u00e7a \u00e9 650N. <\/b><\/span><\/span><\/span>Considere <\/b><\/span><\/span><\/span>g = 10 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

a) Supondo que a for\u00e7a exercida pela bengala sobre a pessoa seja vertical, <\/b><\/span><\/span><\/span>calcule o seu <\/b><\/span><\/span><\/span>m\u00f3dulo e determine o seu sentido.<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>Calcule o <\/b><\/span><\/span><\/span>m\u00f3dulo da for\u00e7a que a balan\u00e7a exerce sobre a pessoa <\/b><\/span><\/span><\/span>e determine a <\/b><\/span><\/span><\/span>sua dire\u00e7\u00e3o e o seu sentido.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0\u00a0<\/span><\/p>\n

05-(FUVEST-SP)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Uma <\/b><\/span><\/span><\/span>for\u00e7a de 1newton (1N) <\/b><\/span><\/span><\/span>tem a <\/b><\/span><\/span><\/span>ordem de grandeza do peso <\/b><\/span><\/span><\/span>de:<\/b><\/span><\/span><\/span>\"\"<\/p>\n

a) <\/b><\/span><\/span><\/span>um homem <\/b><\/span><\/span><\/span>adulto<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>uma crian\u00e7a <\/b><\/span><\/span><\/span>rec\u00e9m-nascida<\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>um litro <\/b><\/span><\/span><\/span>de leite<\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>uma xicrinha <\/b><\/span><\/span><\/span>cheia de caf\u00e9<\/b><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>uma <\/b><\/span><\/span><\/span>moeda<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

06-(FGV-SP)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Durante a <\/b><\/span><\/span><\/span>cerim\u00f4nia de formatura, <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>professor de f\u00edsica, <\/b><\/span><\/span><\/span>teve seu <\/b><\/span><\/span><\/span>pensamento absorvido pela pilha <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

de duas camadas de<\/b><\/span><\/span><\/span> <\/b>estojos de diplomas, <\/b><\/span><\/span><\/span>todos <\/b><\/span><\/span><\/span>iguais, escorada de ambos os lados, por um copo contendo \u00e1gua.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>professor <\/b><\/span><\/span><\/span>lembrava que <\/b><\/span><\/span><\/span>sen 30<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sup><\/span>= cos 60<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sup><\/span>= 1\/2 e que sen 60 <\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>= cos 30<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sup><\/span>= \u221a3\/2. <\/b><\/span><\/span><\/span><\/p>\n

Admitindo que <\/b><\/span><\/span><\/span>cada estojo tivesse o mesmo peso de m\u00f3dulo P<\/b><\/span><\/span><\/span>, determinou <\/b><\/span><\/span><\/span>mentalmente<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>intensidade da for\u00e7a de contato<\/b><\/span><\/span><\/span> exercida por <\/b><\/span><\/span><\/span>um estojo da fila superior sobre um da fila inferior, for\u00e7a<\/b><\/span><\/span><\/span> que, <\/b><\/span><\/span><\/span>escrita em termos de P<\/b><\/span><\/span><\/span>, \u00e9<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span>(\u221a3\/6)P\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>(\u221a3\/3)P\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>(\u221a3)P\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>P\/4\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>P\/2\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

07-(UEG-GO)\u00a0<\/b><\/span><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Entre os <\/b><\/span><\/span><\/span>poucos animais que desenvolveram <\/b><\/span><\/span><\/span>o \u201cp\u00e1ra-quedismo\u201d est\u00e1 o <\/b><\/span><\/span><\/span>sapo voador de Born\u00e9u <\/b><\/span><\/span><\/span>\u2013 <\/b><\/span><\/span><\/span>Rhacophorus dulitensis, <\/b><\/span><\/span><\/span>apresentado na <\/b><\/span><\/span><\/span>figura a seguir.<\/b><\/span><\/span><\/span><\/p>\n

Na ilustra\u00e7\u00e3o,\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0e\u00a0\"\"\u00a0<\/b><\/span><\/span><\/span>s\u00e3o, <\/b><\/span><\/span><\/span>respectivamente, a <\/b><\/span><\/span><\/span>for\u00e7a de resist\u00eancia do ar e a for\u00e7a peso.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Considerando que esse <\/b><\/span><\/span><\/span>animal tenha se atirado do alto de uma \u00e1rvore em dire\u00e7\u00e3o ao solo,<\/b><\/span><\/span><\/span> o seu <\/b><\/span><\/span><\/span>p\u00e1ra-quedas ser\u00e1 utilizado <\/b><\/span><\/span><\/span>e, <\/b><\/span><\/span><\/span>durante sua queda,<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span>as suas <\/b><\/span><\/span><\/span>membranas interdigitais <\/b><\/span><\/span><\/span>nas patas <\/b><\/span><\/span><\/span>favorecem o aumento da for\u00e7a de resist\u00eancia do ar, <\/b><\/span><\/span><\/span>haja vista que elas <\/b><\/span><\/span><\/span>aumentam a \u00e1rea de contato com o ar.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>resultante das for\u00e7as <\/b><\/span><\/span><\/span>que atuam sobre ele <\/b><\/span><\/span><\/span>tender\u00e1 a se tornar nula, levando-o, necessariamente,<\/b><\/span><\/span><\/span> ao <\/b><\/span><\/span><\/span>repouso no ar.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>a sua <\/b><\/span><\/span><\/span>velocidade tender\u00e1 a um valor limite, <\/b><\/span><\/span><\/span>chamada de <\/b><\/span><\/span><\/span>velocidade terminal, independentemente da resist\u00eancia do ar.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>a sua <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o ser\u00e1 nula<\/b><\/span><\/span><\/span> em todo o <\/b><\/span><\/span><\/span>percurso, independentemente da resist\u00eancia do ar.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

08-(UFABC)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>mec\u00e2nico afirma <\/b><\/span><\/span><\/span>ao <\/b><\/span><\/span><\/span>seu assistente <\/b><\/span><\/span><\/span>que \u00e9 <\/b><\/span><\/span><\/span>poss\u00edvel erguer e manter um carro no alto <\/b><\/span><\/span><\/span>e em <\/b><\/span><\/span><\/span>equil\u00edbrio est\u00e1tico,<\/b><\/span><\/span><\/span> usando-se um <\/b><\/span><\/span><\/span>contrapeso mais leve do que o carro. <\/b><\/span><\/span><\/span>\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>figura mostra, fora<\/b><\/span><\/span><\/span> de <\/b><\/span><\/span><\/span>escala,<\/b><\/span><\/span><\/span> o esquema <\/b><\/span><\/span><\/span>sugerido pelo mec\u00e2nico para obter o seu intento.<\/b><\/span><\/span><\/span><\/p>\n

Considerando as <\/b><\/span><\/span><\/span>polias e os cabos como ideais <\/b><\/span><\/span><\/span>e, ainda, os <\/b><\/span><\/span><\/span>cabos convenientemente presos <\/b><\/span><\/span><\/span>ao <\/b><\/span><\/span><\/span>carro <\/b><\/span><\/span><\/span>para que <\/b><\/span><\/span><\/span>n\u00e3o haja movimento de rota\u00e7\u00e3o, determine a massa m\u00ednima do contrapeso <\/b><\/span><\/span><\/span>e o <\/b><\/span><\/span><\/span>valor da for\u00e7a que o cabo central <\/b><\/span><\/span><\/span>exerce <\/b><\/span><\/span><\/span>sobre o carro, com massa de 700 kg, <\/b><\/span><\/span><\/span>quando esse <\/b><\/span><\/span><\/span>se encontra suspenso e em equil\u00edbrio est\u00e1tico.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

09-(UNIMONTES-MG)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>macaco de 10kg sobe <\/b><\/span><\/span><\/span>por uma <\/b><\/span><\/span><\/span>corda de massa desprez\u00edve<\/b><\/span><\/span><\/span>l, que <\/b><\/span><\/span><\/span>passa sobre o galho de uma \u00e1rvore (veja a figura).<\/b><\/span><\/span><\/span>\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>corda pode deslizar, sem atrito, <\/b><\/span><\/span><\/span>sobre a <\/b><\/span><\/span><\/span>superf\u00edcie do galho.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

A <\/b><\/span><\/span><\/span>outra extremidade da corda est\u00e1 presa a uma caixa <\/b><\/span><\/span><\/span>cuja <\/b><\/span><\/span><\/span>massa \u00e9 15 kg. <\/b><\/span><\/span><\/span>O <\/b><\/span><\/span><\/span>menor valor do m\u00f3dulo <\/b><\/span><\/span><\/span>da <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o que o macaco deve ter ao subir pela corda<\/b><\/span><\/span><\/span>, para <\/b><\/span><\/span><\/span>erguer a caixa, <\/b><\/span><\/span><\/span>\u00e9 igual a: Dado: <\/b><\/span><\/span><\/span>g = 9,8 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span>9,8 m\/s<\/b><\/span><\/span><\/span>2\u00a0<\/b><\/span><\/span><\/sup><\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>2,4 m\/s<\/b><\/span><\/span><\/span>2\u00a0<\/b><\/span><\/span><\/sup><\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>7,3 m\/s<\/b><\/span><\/span><\/span>2\u00a0<\/b><\/span><\/span><\/sup><\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>4,9 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>zero<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

10-(ITA-SP)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Uma <\/b><\/span><\/span><\/span>pilha de seis blocos iguais, <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>mesma massa m, repousa <\/b><\/span><\/span><\/span>sobre o <\/b><\/span><\/span><\/span>piso de um elevador, <\/b><\/span><\/span><\/span>como mostra a <\/b><\/span><\/span><\/span>figura.<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>elevador est\u00e1 subindo em movimento uniformemente retardado <\/b><\/span><\/span><\/span>com <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o<\/b><\/span><\/span><\/span> de <\/b><\/span><\/span><\/span>m\u00f3dulo a.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

O <\/b><\/span><\/span><\/span>m\u00f3dulo da for\u00e7a que o bloco 3 exerce sobre o bloco 2 <\/b><\/span><\/span><\/span>\u00e9 dado por:<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span>3m(g + a)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>3m(g \u2013 a)\u00a0\u00a0\u00a0 \u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span> <\/b><\/p>\n

c) <\/b><\/span><\/span><\/span>2m(g + a)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>2m(g \u2013 a)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>m(2g \u2013 a)<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

11-(PUC-MG)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Muitos carros e transportes modernos <\/b><\/span><\/span><\/span>est\u00e3o <\/b><\/span><\/span><\/span>equipados com um sistema de frenagem <\/b><\/span><\/span><\/span>intitulado <\/b><\/span><\/span><\/span>ABS, que evita que o pneu deslize quando os freios forem acionados. <\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>sistema funciona <\/b><\/span><\/span><\/span>atrav\u00e9s de <\/b><\/span><\/span><\/span>um sensor que verifica, dezenas de vezes por segundo<\/b><\/span><\/span><\/span>, se a <\/b><\/span><\/span><\/span>roda <\/b><\/span><\/span><\/span>\u201ctravou\u201d, ou seja, <\/b><\/span><\/span><\/span>parou de girar. <\/b><\/span><\/span><\/span>\"\"<\/p>\n

Se <\/b><\/span><\/span><\/span>isso ocorrer<\/b><\/span><\/span><\/span>, ele <\/b><\/span><\/span><\/span>momentaneamente libera aquela roda da a\u00e7\u00e3o do freio, <\/b><\/span><\/span><\/span>para <\/b><\/span><\/span><\/span>s\u00f3 voltar a aplic\u00e1-lo <\/b><\/span><\/span><\/span>quando a <\/b><\/span><\/span><\/span>roda retomar seu movimento normal de rota\u00e7\u00e3o.<\/b><\/span><\/span><\/span><\/p>\n

Esse <\/b><\/span><\/span><\/span>sistema <\/b><\/span><\/span><\/span>garante <\/b><\/span><\/span><\/span>frenagens mais seguras, <\/b><\/span><\/span><\/span>e em <\/b><\/span><\/span><\/span>espa\u00e7o menor, <\/b><\/span><\/span><\/span>porque:<\/b><\/span><\/span><\/span><\/p>\n

a)\u00a0<\/b><\/span><\/span><\/span>quando a <\/b><\/span><\/span><\/span>roda \u201ctrava\u201d, <\/b><\/span><\/span><\/span>h\u00e1 uma <\/b><\/span><\/span><\/span>perda de energia mec\u00e2nica do sistema que deve ser evitada.<\/b><\/span><\/span><\/span><\/p>\n

b)\u00a0<\/b><\/span><\/span><\/span>quando a <\/b><\/span><\/span><\/span>roda \u201ctrava\u201d, <\/b><\/span><\/span><\/span>h\u00e1 um <\/b><\/span><\/span><\/span>superaquecimento do sistema de freios que deve ser evitado.<\/b><\/span><\/span><\/span><\/p>\n

c)\u00a0<\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>in\u00e9rcia do carro \u00e9 maior <\/b><\/span><\/span><\/span>com a <\/b><\/span><\/span><\/span>roda \u201ctravada\u201d do que com a roda girando.<\/b><\/span><\/span><\/span><\/p>\n

d)\u00a0a dirigibilidade do carro \u00e9 maior com a roda \u201ctravada\u201d do que com <\/b><\/span><\/span><\/span>a roda girando.<\/b><\/span><\/span><\/span><\/p>\n

e)\u00a0<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>coeficiente de atrito est\u00e1tico \u00e9 maior que o coeficiente de atrito cin\u00e9tico.<\/b><\/span><\/span><\/span><\/p>\n

12-(PUC-RJ)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Uma <\/b><\/span><\/span><\/span>locomotiva puxa uma s\u00e9rie de vag\u00f5es, <\/b><\/span><\/span><\/span>a partir do <\/b><\/span><\/span><\/span>repouso.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Qual \u00e9 a <\/b><\/span><\/span><\/span>an\u00e1lise correta da situa\u00e7\u00e3o?<\/b><\/span><\/span><\/span><\/p>\n

a)\u00a0<\/b><\/span><\/span><\/span>A <\/b><\/span><\/span><\/span>locomotiva <\/b><\/span><\/span><\/span>pode <\/b><\/span><\/span><\/span>mover o trem somente <\/b><\/span><\/span><\/span>se for <\/b><\/span><\/span><\/span>mais pesada do que os vag\u00f5es.<\/b><\/span><\/span><\/span><\/p>\n

b)\u00a0<\/b><\/span><\/span><\/span>A <\/b><\/span><\/span><\/span>for\u00e7a que a locomotiva <\/b><\/span><\/span><\/span>exerce nos <\/b><\/span><\/span><\/span>vag\u00f5es \u00e9 t\u00e3o intensa quanto <\/b><\/span><\/span><\/span>a que os <\/b><\/span><\/span><\/span>vag\u00f5es exercem <\/b><\/span><\/span><\/span>na <\/b><\/span><\/span><\/span>locomotiva;<\/b><\/span><\/span><\/span> no <\/b><\/span><\/span><\/span>entanto, a for\u00e7a de atrito na locomotiva \u00e9 grande <\/b><\/span><\/span><\/span>e \u00e9 <\/b><\/span><\/span><\/span>para frente<\/b><\/span><\/span><\/span>, enquanto que a que <\/b><\/span><\/span><\/span>ocorre nos vag\u00f5es \u00e9 pequena e para tr\u00e1s.<\/b><\/span><\/span><\/span><\/p>\n

c)\u00a0<\/b><\/span><\/span><\/span>O <\/b><\/span><\/span><\/span>trem se move porque a locomotiva d\u00e1 um r\u00e1pido pux\u00e3o nos vag\u00f5es,<\/b><\/span><\/span><\/span> e, momentaneamente, <\/b><\/span><\/span><\/span>esta for\u00e7a \u00e9 maior do que a que os vag\u00f5es exercem na locomotiva.<\/b><\/span><\/span><\/span><\/p>\n

d)\u00a0<\/b><\/span><\/span><\/span>O <\/b><\/span><\/span><\/span>trem se move para frente <\/b><\/span><\/span><\/span>porque a locomotiva <\/b><\/span><\/span><\/span>puxa os vag\u00f5es para frente <\/b><\/span><\/span><\/span>com uma <\/b><\/span><\/span><\/span>for\u00e7a maior do que a for\u00e7a com a qual os vag\u00f5es puxam a locomotiva para tr\u00e1s.<\/b><\/span><\/span><\/span><\/p>\n

e)\u00a0<\/b><\/span><\/span><\/span>Porque a <\/b><\/span><\/span><\/span>a\u00e7\u00e3o \u00e9 sempre igual \u00e0 rea\u00e7\u00e3o,<\/b><\/span><\/span><\/span> a locomotiva <\/b><\/span><\/span><\/span>n\u00e3o consegue puxar os vag\u00f5es.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

13- (UFSCAR-SP)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>sistema esquematizado <\/b><\/span><\/span><\/span>comp\u00f5e-se de um <\/b><\/span><\/span><\/span>elevador de massa M <\/b><\/span><\/span><\/span>e um <\/b><\/span><\/span><\/span>homem de massa m. <\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>elevador est\u00e1 suspenso <\/b><\/span><\/span><\/span>por uma corda que <\/b><\/span><\/span><\/span>passa por uma polia fixa <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>vem \u00e0s m\u00e3os do operador; a corda <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>roldana s\u00e3o supostas ideais. \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>operador puxa a corda <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>sobe com acelera\u00e7\u00e3o constante a, juntamente<\/b><\/span><\/span><\/span> com o <\/b><\/span><\/span><\/span>elevador.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

S\u00e3o <\/b><\/span><\/span><\/span>supostos conhecidos M, m, a e g. Determine<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>intensidade da for\u00e7a \"\"que traciona a corda.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

14-(UNESP-SP)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Uma <\/b><\/span><\/span><\/span>barra AC <\/b><\/span><\/span><\/span>homog\u00eanea <\/b><\/span><\/span><\/span>de massa m e comprimento L, <\/b><\/span><\/span><\/span>colocada numa <\/b><\/span><\/span><\/span>mesa lisa e horizontal, desliza sem girar sob a\u00e7\u00e3o de uma for\u00e7a \"\", <\/b><\/span><\/span><\/span>tamb\u00e9m <\/b><\/span><\/span><\/span>horizontal, aplicada na sua extremidade esquerda.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Mostre<\/b><\/span><\/span><\/span> que a <\/b><\/span><\/span><\/span>for\u00e7a \"\"<\/b><\/span><\/span><\/span> com que a <\/b><\/span><\/span><\/span>fra\u00e7\u00e3o BC <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>comprimento (2L\/3), atua <\/b><\/span><\/span><\/span>sobre a <\/b><\/span><\/span><\/span>fra\u00e7\u00e3o AB <\/b><\/span><\/span><\/span>\u00e9 igual a <\/b><\/span><\/span><\/span>(- 2\"\"\/3).<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

15-(PUC-RJ)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Alberto (A) desafiou<\/b><\/span><\/span><\/span> seu colega <\/b><\/span><\/span><\/span>Cabral (C) <\/b><\/span><\/span><\/span>para uma <\/b><\/span><\/span><\/span>competi\u00e7\u00e3o de cabo de guerra,<\/b><\/span><\/span><\/span> de uma <\/b><\/span><\/span><\/span>maneira especial, <\/b><\/span><\/span><\/span>mostrada na <\/b><\/span><\/span><\/span>figura.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Alberto segurou<\/b><\/span><\/span><\/span> no <\/b><\/span><\/span><\/span>peda\u00e7o de corda <\/b><\/span><\/span><\/span>que <\/b><\/span><\/span><\/span>passava ao redor da polia <\/b><\/span><\/span><\/span>enquanto que <\/b><\/span><\/span><\/span>Cabral segurou <\/b><\/span><\/span><\/span>no <\/b><\/span><\/span><\/span>peda\u00e7o atado ao centro da polia. <\/b><\/span><\/span><\/span><\/p>\n

Apesar de <\/b><\/span><\/span><\/span>mais forte, Cabral n\u00e3o conseguiu puxar Alberto, <\/b><\/span><\/span><\/span>que <\/b><\/span><\/span><\/span>lentamente<\/b><\/span><\/span><\/span> foi <\/b><\/span><\/span><\/span>arrastando o seu advers\u00e1rio at\u00e9 ganhar o jogo.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Sabendo que a <\/b><\/span><\/span><\/span>for\u00e7a com que Alberto puxa a corda \u00e9 de 200 N <\/b><\/span><\/span><\/span>e que a <\/b><\/span><\/span><\/span>polia n\u00e3o tem massa nem atritos:<\/b><\/span><\/span><\/span><\/p>\n

a) especifique a tens\u00e3o na corda<\/b><\/span><\/span><\/span> que <\/b><\/span><\/span><\/span>Alberto est\u00e1 segurando;<\/b><\/span><\/span><\/span><\/p>\n

b) desenhe as for\u00e7as <\/b><\/span><\/span><\/span>que <\/b><\/span><\/span><\/span>agem sobre a polia, <\/b><\/span><\/span><\/span>fazendo um <\/b><\/span><\/span><\/span>diagrama de corpo livre;<\/b><\/span><\/span><\/span><\/p>\n

c) calcule a for\u00e7a exercida pelo Cabral sobre a corda que ele puxava;<\/b><\/span><\/span><\/span><\/p>\n

d) considerando que Cabral foi puxado por 2,0 m para frente, <\/b><\/span><\/span><\/span>indique <\/b><\/span><\/span><\/span>quanto Alberto andou para tr\u00e1s.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

16-(UEL-PR)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Considere o <\/b><\/span><\/span><\/span>sistema constitu\u00eddo por tr\u00eas blocos de massas m<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>, m<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0e m<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sub><\/span>, <\/b><\/span><\/span><\/span>apoiados <\/b><\/span><\/span><\/span>um sobre o outro, <\/b><\/span><\/span><\/span>em <\/b><\/span><\/span><\/span>repouso sobre uma superf\u00edcie horizontal, <\/b><\/span><\/span><\/span>como mostra a <\/b><\/span><\/span><\/span>figura<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Observe que <\/b><\/span><\/span><\/span>uma for\u00e7a \"\"\u00a0\u00e9 aplicada ao bloco de massa m<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>, <\/b><\/span><\/span><\/span>conforme a <\/b><\/span><\/span><\/span>representa\u00e7\u00e3o.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Entretanto,<\/b><\/span><\/span><\/span> esta <\/b><\/span><\/span><\/span>for\u00e7a \u00e9 incapaz de vencer as for\u00e7as de f<\/b><\/span><\/span><\/span>ij<\/b><\/span><\/span><\/sub><\/span>\u00a0entre os blocos m<\/b><\/span><\/span><\/span>i<\/b><\/span><\/span><\/sub><\/span>\u00a0e m<\/b><\/span><\/span><\/span>j<\/b><\/span><\/span><\/sub><\/span>, onde i e j variam de 1 a 3.<\/b><\/span><\/span><\/span><\/p>\n

Desprezando a <\/b><\/span><\/span><\/span>resist\u00eancia do ar, <\/b><\/span><\/span><\/span>assinale a <\/b><\/span><\/span><\/span>alternativa que representa todas as for\u00e7as que atuam no bloco de massa m<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>,<\/b><\/span><\/span><\/span> onde os <\/b><\/span><\/span><\/span>N<\/b><\/span><\/span><\/span>i <\/b><\/span><\/span><\/sub><\/span>representam as normais que atuam nos blocos <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>P<\/b><\/span><\/span><\/span>i<\/b><\/span><\/span><\/sub><\/span>, correspondem aos pesos dos respectivos blocos com i variando de 1 a 3.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

17-(UNESP-SP)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>rebocador puxa duas barca\u00e7as pela \u00e1guas de um lago tranq\u00fcilo. <\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>primeira delas tem massa de 30 toneladas <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>segunda, 20 toneladas. <\/b><\/span><\/span><\/span><\/p>\n

Por uma <\/b><\/span><\/span><\/span>quest\u00e3o de economia, o cabo de a\u00e7o I que conecta o rebocador \u00e0 primeira barca\u00e7a suporta, <\/b><\/span><\/span><\/span>no <\/b><\/span><\/span><\/span>m\u00e1ximo, 6.10<\/b><\/span><\/span><\/span>5 <\/b><\/span><\/span><\/sup><\/span>N, e o cabo II, 8.10<\/b><\/span><\/span><\/span>4 <\/b><\/span><\/span><\/sup><\/span>N.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Desprezando <\/b><\/span><\/span><\/span>o efeito de <\/b><\/span><\/span><\/span>for\u00e7as resistivas, <\/b><\/span><\/span><\/span>calcule a <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o m\u00e1xima do conjunto, a fim de evitar o rompimento de um dos cabos.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

18-(FUVEST-SP)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

19-(UERJ-RJ)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>figura abaixo <\/b><\/span><\/span><\/span>representa o <\/b><\/span><\/span><\/span>plano inclinado ABFE, inserido<\/b><\/span><\/span><\/span> em um <\/b><\/span><\/span><\/span>paralelep\u00edpedo ret\u00e2ngulo ABCDEFGH de base horizontal, com 6 m de altura CF, 8 m de comprimento BC e 15 m de largura AB, em repouso, <\/b><\/span><\/span><\/span>apoiado no solo.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Considere o <\/b><\/span><\/span><\/span>deslocamento em movimento retil\u00edneo de um corpo P<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0de M at\u00e9 N e de um corpo P<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0de A at\u00e9 F.<\/b><\/span><\/span><\/span><\/p>\n

Admita as <\/b><\/span><\/span><\/span>seguintes informa\u00e7\u00f5es:<\/b><\/span><\/span><\/span><\/p>\n

– P<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0e P<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0s\u00e3o corpos id\u00eanticos;<\/b><\/span><\/span><\/span><\/p>\n

– F<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0e F<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0<\/b><\/span><\/span><\/span>s\u00e3o, <\/b><\/span><\/span><\/span>respectivamente, as componentes dos pesos de P<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0e P<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0ao longo das respectivas trajet\u00f3rias;<\/b><\/span><\/span><\/span><\/p>\n

– M e N s\u00e3o, respectivamente, os pontos m\u00e9dios das arestas AB e EF.<\/b><\/span><\/span><\/span><\/p>\n

Considerando <\/b><\/span><\/span><\/span>esses dados, a raz\u00e3o F<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\/F<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0equivale a:<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

20-(UFG-GO)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

No <\/b><\/span><\/span><\/span>sistema representado na figura,<\/b><\/span><\/span><\/span> as <\/b><\/span><\/span><\/span>duas molas s\u00e3o iguais, t\u00eam 1 m de comprimento <\/b><\/span><\/span><\/span>e est\u00e3o <\/b><\/span><\/span><\/span>relaxadas. <\/b><\/span><\/span><\/span>Quando o <\/b><\/span><\/span><\/span>fio \u00e9 cortado<\/b><\/span><\/span><\/span>, a esfera de <\/b><\/span><\/span><\/span>massa 5,1 kg desce 1 m at\u00e9 parar momentaneamente.<\/b><\/span><\/span><\/span><\/p>\n

Dados: \u221a<\/b><\/span><\/span><\/span>2=1,41 e g=10m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Calcule<\/b><\/span><\/span><\/span> o <\/b><\/span><\/span><\/span>valor da constante el\u00e1stica k das molas.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

21-(EFB)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>mola helicoidal (figura 1), de constante el\u00e1stica k=12N\/m,<\/b><\/span><\/span><\/span> foi <\/b><\/span><\/span><\/span>partida em 3 partes iguais. <\/b><\/span><\/span><\/span><\/p>\n

Em seguida, <\/b><\/span><\/span><\/span>essas 3 partes foram associadas em paralelo (figura 2) e em s\u00e9rie (figura 3).\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

As <\/b><\/span><\/span><\/span>massas das figuras 2 e 3 <\/b><\/span><\/span><\/span>s\u00e3o <\/b><\/span><\/span><\/span>iguais e valem 100g. <\/b><\/span><\/span><\/span><\/p>\n

Adote <\/b><\/span><\/span><\/span>g = 10m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0<\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>determine:<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>constante el\u00e1stica <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>cada parte.<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>per\u00edodo<\/b><\/span><\/span><\/span> de <\/b><\/span><\/span><\/span>oscila\u00e7\u00e3o<\/b><\/span><\/span><\/span> do <\/b><\/span><\/span><\/span>conjunto quando as tr\u00eas molas est\u00e3o associadas em paralelo.<\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>per\u00edodo<\/b><\/span><\/span><\/span> de <\/b><\/span><\/span><\/span>oscila\u00e7\u00e3o<\/b><\/span><\/span><\/span> do <\/b><\/span><\/span><\/span>conjunto quando as tr\u00eas molas est\u00e3o associadas em s\u00e9rie.<\/b><\/span><\/span><\/span><\/p>\n

22-(UFRS-RS)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>figura <\/b><\/span><\/span><\/span>representa <\/b><\/span><\/span><\/span>seis p\u00eandulos simples, <\/b><\/span><\/span><\/span>que est\u00e3o <\/b><\/span><\/span><\/span>oscilando num mesmo local.<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>p\u00eandulo P executa uma oscila\u00e7\u00e3o completa em 2 s. <\/b><\/span><\/span><\/span><\/p>\n

Qual dos outros p\u00eandulos executa uma oscila\u00e7\u00e3o completa em 1 s?<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span>I.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>II.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>III.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>IV.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>V.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

23-(ITA-SP)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>p\u00eandulo simples <\/b><\/span><\/span><\/span>oscila com um <\/b><\/span><\/span><\/span>per\u00edodo de 2s<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span><\/p>\n

Se <\/b><\/span><\/span><\/span>cravarmos um pino a uma dist\u00e2ncia 3L\/4 do ponto de suspens\u00e3o<\/b><\/span><\/span><\/span> e <\/b><\/span><\/span><\/span>na vertical que passa por aquele ponto,<\/b><\/span><\/span><\/span> como <\/b><\/span><\/span><\/span>mostrado na figura, qual ser\u00e1 o novo per\u00edodo do p\u00eandulo?<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

24-(ITA-SP )<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

25-(ITA-SP)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>rel\u00f3gio tem um p\u00eandulo de 35 cm de comprimento.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Para <\/b><\/span><\/span><\/span>regular<\/b><\/span><\/span><\/span> seu funcionamento, ele <\/b><\/span><\/span><\/span>possui uma porca de ajuste<\/b><\/span><\/span><\/span> que <\/b><\/span><\/span><\/span>encurta o comprimento do pendulo de 1 mm a cada rota\u00e7\u00e3o completa \u00e0 direita <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>alonga este comprimento de 1 mm a cada rota\u00e7\u00e3o completa \u00e0 esquerda.<\/b><\/span><\/span><\/span><\/p>\n

Se o <\/b><\/span><\/span><\/span>rel\u00f3gio atrasa um minuto por dia,<\/b><\/span><\/span><\/span> indique o <\/b><\/span><\/span><\/span>n\u00famero aproximado de rota\u00e7\u00f5es da porca <\/b><\/span><\/span><\/span>e sua <\/b><\/span><\/span><\/span>dire\u00e7\u00e3o necess\u00e1rios para que ele funcione corretamente.<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span>1 rota\u00e7\u00e3o \u00e0 esquerda \u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>1\/2 rota\u00e7\u00e3o \u00e0 esquerda \u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>1\/2 rota\u00e7\u00e3o \u00e0 direita \u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>1 rota\u00e7\u00e3o \u00e0 direita \u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>1 e 1\/2 rota\u00e7\u00f5es \u00e0 direita.<\/b><\/span><\/span><\/span><\/p>\n

26-(UFJF-MG)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>caminh\u00e3o \u00e9 carregado com duas caixas\u00a0 de madeira, <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>massas iguais a 500kg, <\/b><\/span><\/span><\/span>conforme mostra a <\/b><\/span><\/span><\/span>figura.<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>caminh\u00e3o \u00e9 ent\u00e3o posto em movimento <\/b><\/span><\/span><\/span>numa <\/b><\/span><\/span><\/span>estrada reta e plana, acelerando <\/b><\/span><\/span><\/span>at\u00e9 adquirir uma <\/b><\/span><\/span><\/span>velocidade de 108km\/h e <\/b><\/span><\/span><\/span>depois \u00e9 <\/b><\/span><\/span><\/span>freado at\u00e9 parar, <\/b><\/span><\/span><\/span>conforme mostra o <\/b><\/span><\/span><\/span>gr\u00e1fico. (g = 10 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>).<\/b><\/span><\/span><\/span><\/p>\n

\"\"\"\"<\/p>\n

O coeficiente de atrito est\u00e1tico entre as caixas e a carroceria do caminh\u00e3o \u00e9 \u03bc=0,1. Qual das figuras abaixo melhor representa a disposi\u00e7\u00e3o das caixas sobre a carroceria no final do movimento?<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0<\/span><\/p>\n

27-(ENEM-MEC<\/b><\/span><\/span><\/span>)\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Os <\/b><\/span><\/span><\/span>freios ABS <\/b><\/span><\/span><\/span>s\u00e3o uma <\/b><\/span><\/span><\/span>importante medida de seguran\u00e7a no tr\u00e2nsito, <\/b><\/span><\/span><\/span>os quais f<\/b><\/span><\/span><\/span>uncionam<\/b><\/span><\/span><\/span> para <\/b><\/span><\/span><\/span>impedir o travamento das rodas do carro <\/b><\/span><\/span><\/span>quando o <\/b><\/span><\/span><\/span>sistema de freios \u00e9 acionado,<\/b><\/span><\/span><\/span> <\/b>liberando<\/b><\/span><\/span><\/span> as rodas quando est\u00e3o no <\/b><\/span><\/span><\/span>limiar do deslizamento. <\/b><\/span><\/span><\/span><\/p>\n

Quando as <\/b><\/span><\/span><\/span>rodas travam, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>for\u00e7a de frenagem \u00e9 governada pelo atrito cin\u00e9tico.<\/b><\/span><\/span><\/span><\/p>\n

As <\/b><\/span><\/span><\/span>representa\u00e7\u00f5es esquem\u00e1ticas da for\u00e7a de atrito f<\/b><\/span><\/span><\/span>at<\/b><\/span><\/span><\/sub><\/span>\u00a0entre os pneus e a pista, <\/b><\/span><\/span><\/span>em <\/b><\/span><\/span><\/span>fun\u00e7\u00e3o da press\u00e3o p aplicada no pedal de freio<\/b><\/span><\/span><\/span>, para <\/b><\/span><\/span><\/span>carros sem ABS <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>com ABS, respectivamente<\/b><\/span><\/span><\/span>, s\u00e3o<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0<\/span><\/p>\n

28-(UPE-PE)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0Sejam os <\/b><\/span><\/span><\/span>blocos P e Q de massas m e M, respectivamente<\/b><\/span><\/span><\/span>, ilustrados na <\/b><\/span><\/span><\/span>figura.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

O <\/b><\/span><\/span><\/span>coeficiente<\/b><\/span><\/span><\/span> de <\/b><\/span><\/span><\/span>atrito est\u00e1tico<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

entre os <\/b><\/span><\/span><\/span>blocos \u00e9 \u03bc, entretanto n\u00e3o existe atrito entre o bloco Q e a superf\u00edcie A.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Considere <\/b><\/span><\/span><\/span>g<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o da gravidade.<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>express\u00e3o que representa o menor valor <\/b><\/span><\/span><\/span>do <\/b><\/span><\/span><\/span>m\u00f3dulo da for\u00e7a horizontal\u00a0\"\"\u00a0para que o bloco P n\u00e3o caia, \u00e9<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0<\/span><\/p>\n

29-(UFF-RJ)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>pano de prato retangular, <\/b><\/span><\/span><\/span>com <\/b><\/span><\/span><\/span>60cm de comprimento e constitui\u00e7\u00e3o homog\u00eanea<\/b><\/span><\/span><\/span>, est\u00e1 em <\/b><\/span><\/span><\/span>repouso sobre uma mesa, <\/b><\/span><\/span><\/span>parte <\/b><\/span><\/span><\/span>sobre sua superf\u00edcie, horizontal e fina, e parte pendente, como mostra a figura.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Sabendo-se que o <\/b><\/span><\/span><\/span>coeficiente de atrito est\u00e1tico entre a superf\u00edcie da mesa\u00a0 e o pano \u00e9 igual a 0,5 <\/b><\/span><\/span><\/span>e que o <\/b><\/span><\/span><\/span>pano est\u00e1 na imin\u00eancia de deslizar,<\/b><\/span><\/span><\/span> pode-se <\/b><\/span><\/span><\/span>afirmar que o comprimento L da parte sobre a mesa <\/b><\/span><\/span><\/span>\u00e9:<\/b><\/span><\/span><\/span><\/p>\n

a) <\/b><\/span><\/span><\/span>40cm\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>20cm\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>15cm\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>60cm\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>30cm<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

30-(ITA-SP)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Para um <\/b><\/span><\/span><\/span>avi\u00e3o executar uma curva nivelada <\/b><\/span><\/span><\/span>(sem subir ou descer) e <\/b><\/span><\/span><\/span>equilibrada,<\/b><\/span><\/span><\/span> o piloto <\/b><\/span><\/span><\/span>deve inclin\u00e1-lo com respeito \u00e0 horizontal <\/b><\/span><\/span><\/span>(\u00e0 maneira de um ciclista em uma curva), de <\/b><\/span><\/span><\/span>um \u00e2ngulo\u00a0\u03b1. <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Se\u00a0<\/b><\/span><\/span><\/span>\u03b1 = 60\u00b0, a \u00a0velocidade da aeronave \u00e9 100 m\/s <\/b><\/span><\/span><\/span>e<\/b><\/span><\/span><\/span><\/p>\n

a <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o local da gravidade <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>9,5 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>, <\/b><\/span><\/span><\/span>qual \u00e9 <\/b><\/span><\/span><\/span>aproximadamente o raio de curvatura?<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

31-(FUVEST-SP)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Uma <\/b><\/span><\/span><\/span>esta\u00e7\u00e3o espacial, <\/b><\/span><\/span><\/span>constru\u00edda em <\/b><\/span><\/span><\/span>forma cil\u00edndrica, <\/b><\/span><\/span><\/span>foi projetada para <\/b><\/span><\/span><\/span>contornar a aus\u00eancia de gravidade no espa\u00e7o.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>figura <\/b><\/span><\/span><\/span>mostra, de maneira <\/b><\/span><\/span><\/span>simplificada, a sec\u00e7\u00e3o reta dessa esta\u00e7\u00e3o, <\/b><\/span><\/span><\/span>que possui <\/b><\/span><\/span><\/span>dois andares.<\/b><\/span><\/span><\/span><\/p>\n

Para <\/b><\/span><\/span><\/span>simular a gravidade, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>esta\u00e7\u00e3o deve girar em torno <\/b><\/span><\/span><\/span>do seu <\/b><\/span><\/span><\/span>eixo com certa velocidade angular. <\/b><\/span><\/span><\/span><\/p>\n

Se o <\/b><\/span><\/span><\/span>raio externo da esta\u00e7\u00e3o \u00e9 R,<\/b><\/span><\/span><\/span><\/p>\n

a) deduza a velocidade angular W <\/b><\/span><\/span><\/span>com que a <\/b><\/span><\/span><\/span>esta\u00e7\u00e3o deve girar para que um astronauta<\/b><\/span><\/span><\/span>, em <\/b><\/span><\/span><\/span>repouso no primeiro andar <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>uma dist\u00e2ncia R do eixo da esta\u00e7\u00e3o, <\/b><\/span><\/span><\/span>fique sujeito a <\/b><\/span><\/span><\/span>uma acelera\u00e7\u00e3o igual a g.<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>Suponha que o <\/b><\/span><\/span><\/span>astronauta v\u00e1 para o segundo andar, <\/b><\/span><\/span><\/span>a uma <\/b><\/span><\/span><\/span>dist\u00e2ncia h do piso do andar anterior. <\/b><\/span><\/span><\/span>Calcule o <\/b><\/span><\/span><\/span>peso do astronauta nessa posi\u00e7\u00e3o <\/b><\/span><\/span><\/span>e compare com o <\/b><\/span><\/span><\/span>seu peso quando estava no primeiro andar.<\/b><\/span><\/span><\/span> O <\/b><\/span><\/span><\/span>peso aumenta, diminui ou permanece inalterado ?<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

32-(UFOP-MG)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Uma <\/b><\/span><\/span><\/span>esta\u00e7\u00e3o espacial \u00e9 projetada <\/b><\/span><\/span><\/span>como sendo um <\/b><\/span><\/span><\/span>cilindro de raio r<\/b><\/span><\/span><\/span>, que <\/b><\/span><\/span><\/span>gira em seu eixo<\/b><\/span><\/span><\/span> com <\/b><\/span><\/span><\/span>velocidade angular constante W, <\/b><\/span><\/span><\/span>de modo a <\/b><\/span><\/span><\/span>produzir uma sensa\u00e7\u00e3o de gravidade de 1g = 9,8 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0nos p\u00e9s de uma pessoa que est\u00e1 no<\/b><\/span><\/span><\/span>\"\"<\/p>\n

interior da esta\u00e7\u00e3o.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Admitindo-se que os <\/b><\/span><\/span><\/span>seus habitantes t\u00eam uma altura m\u00e9dia de h = 2 m, <\/b><\/span><\/span><\/span>qual deve ser o <\/b><\/span><\/span><\/span>raio m\u00ednimo r da esta\u00e7\u00e3o, <\/b><\/span><\/span><\/span>de modo que a <\/b><\/span><\/span><\/span>varia\u00e7\u00e3o da gravidade sentida entre os p\u00e9s e a cabe\u00e7a seja inferior a 1% de g?<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

33-(UFPE-PE)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>bloco\u00a0A\u00a0de massa igual a\u00a01kg\u00a0<\/b><\/span><\/span><\/span>\u00e9 mantido em <\/b><\/span><\/span><\/span>repouso,<\/b><\/span><\/span><\/span> em <\/b><\/span><\/span><\/span>contato com o teto <\/b><\/span><\/span><\/span>de um <\/b><\/span><\/span><\/span>apartamento, <\/b><\/span><\/span><\/span>sob o efeito de uma <\/b><\/span><\/span><\/span>for\u00e7a\u00a0\"\"\u00a0de intensidade F = 20 N\u00a0<\/b><\/span><\/span><\/span>como ilustrado <\/b><\/span><\/span><\/span>na figura.<\/b><\/span><\/span><\/span><\/p>\n

Sabendo-se que\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0\u00e9 a for\u00e7a de rea\u00e7\u00e3o normal \u00e0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

superf\u00edcie do teto<\/b><\/span><\/span><\/span>,<\/b><\/span><\/span><\/span> \"\" <\/b><\/span><\/span><\/span>\u00e9 o <\/b><\/span><\/span><\/span>peso do bloco<\/b><\/span><\/span><\/span>, e \"\"<\/b><\/span><\/span><\/span> \u00e9 a for\u00e7a de atrito, <\/b><\/span><\/span><\/span>qual o <\/b><\/span><\/span><\/span>diagrama das for\u00e7as que atuam sobre o bloco\u00a0A?<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0<\/span><\/p>\n

34-(UFG-GO)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Nas <\/b><\/span><\/span><\/span>academias de gin\u00e1stica, <\/b><\/span><\/span><\/span>usa-se um <\/b><\/span><\/span><\/span>aparelho chamado press\u00e3o com pernas <\/b><\/span><\/span><\/span>(leg press), que tem a <\/b><\/span><\/span><\/span>fun\u00e7\u00e3o de fortalecer a musculatura das pernas.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Este <\/b><\/span><\/span><\/span>aparelho possui uma parte m\u00f3vel <\/b><\/span><\/span><\/span>que <\/b><\/span><\/span><\/span>desliza sobre um plano inclinado, <\/b><\/span><\/span><\/span>fazendo um <\/b><\/span><\/span><\/span>\u00e2ngulo de 60\u00ba com a horizontal. <\/b><\/span><\/span><\/span><\/p>\n

Uma <\/b><\/span><\/span><\/span>pessoa,<\/b><\/span><\/span><\/span> usando o <\/b><\/span><\/span><\/span>aparelho,<\/b><\/span><\/span><\/span> empurra a <\/b><\/span><\/span><\/span>parte m\u00f3vel de massa igual 100 kg <\/b><\/span><\/span><\/span>e a faz <\/b><\/span><\/span><\/span>mover<\/b><\/span><\/span><\/span> ao <\/b><\/span><\/span><\/span>longo do plano, com velocidade constante <\/b><\/span><\/span><\/span>como \u00e9 mostrado na <\/b><\/span><\/span><\/span>figura.<\/b><\/span><\/span><\/span><\/p>\n

Considere o <\/b><\/span><\/span><\/span>coeficiente de atrito din\u00e2mico entre o plano inclinado<\/b><\/span><\/span><\/span> e a <\/b><\/span><\/span><\/span>parte m\u00f3vel 0,10<\/b><\/span><\/span><\/span> e a <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o<\/b><\/span><\/span><\/span> <\/b>gravitacional 10m\/s\u00b2. <\/b><\/span><\/span><\/span>(Usar sen60\u00ba = 0,86 e cos60\u00ba = 0,50).
\n<\/b><\/span><\/span><\/span>a) <\/b><\/span><\/span><\/span>Fa\u00e7a o <\/b><\/span><\/span><\/span>diagrama das for\u00e7as que est\u00e3o atuando sobre a parte m\u00f3vel do aparelho identificando-as.
\nb) <\/b><\/span><\/span><\/span>Determine a <\/b><\/span><\/span><\/span>intensidade da for\u00e7a que pessoa est\u00e1 aplicando sobre a parte m\u00f3vel do aparelho.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

35-(FISICAEVESTIBULAR)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>figura abaixo <\/b><\/span><\/span><\/span>mostra um <\/b><\/span><\/span><\/span>carrinho de brinquedo <\/b><\/span><\/span><\/span>se <\/b><\/span><\/span><\/span>deslocando com acelera\u00e7\u00e3o constante de 6,0 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0numa superf\u00edcie plana e horizontal.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>esfera E possui massa de 1 kg <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>n\u00e3o existe atrito entre ela e o plano inclinado <\/b><\/span><\/span><\/span>no qual ela est\u00e1 apoiada. <\/b><\/span><\/span><\/span><\/p>\n

Considere <\/b><\/span><\/span><\/span>sen30<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sup><\/span>= 0,5, cos30<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sup><\/span>= 0,87 e g=10m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>. <\/b><\/span><\/span><\/span>Considere a <\/b><\/span><\/span><\/span>esfera E em repouso <\/b><\/span><\/span><\/span>em <\/b><\/span><\/span><\/span>rela\u00e7\u00e3o <\/b><\/span><\/span><\/span>ao <\/b><\/span><\/span><\/span>carrinho e determine a intensidade da for\u00e7a horizontal que a parede\u00a0 vertical do carrinho exerce sobre a esfera.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

36-(UFV\/MG)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>objeto de massa m repousa<\/b><\/span><\/span><\/span> sobre um <\/b><\/span><\/span><\/span>bloco de massa M, <\/b><\/span><\/span><\/span>que \u00e9 <\/b><\/span><\/span><\/span>empurrado contra uma parede <\/b><\/span><\/span><\/span>por uma <\/b><\/span><\/span><\/span>for\u00e7a horizontal\u00a0\"\", <\/b><\/span><\/span><\/span>conforme mostra a <\/b><\/span><\/span><\/span>figura.<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>coeficiente de atrito est\u00e1tico <\/b><\/span><\/span><\/span>entre o <\/b><\/span><\/span><\/span>bloco e a parede \u00e9 \u03bc\u00a0<\/b><\/span><\/span><\/span>e o <\/b><\/span><\/span><\/span>m\u00f3dulo da acelera\u00e7\u00e3o da gravidade <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>g. <\/b><\/span><\/span><\/span><\/p>\n

Estando o <\/b><\/span><\/span><\/span>sistema em equil\u00edbrio, <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>CORRETO a<\/b><\/span><\/span><\/span>firmar que o <\/b><\/span><\/span><\/span>m\u00f3dulo da for\u00e7a\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0\u00e9<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0<\/span><\/p>\n

37-(UNCISAL-AL)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A\u00a0<\/b><\/span><\/span><\/span>aferi\u00e7\u00e3o da massa\u00a0de uma pessoa <\/b><\/span><\/span><\/span>pode ser <\/b><\/span><\/span><\/span>realizada<\/b><\/span><\/span><\/span> por meio de uma\u00a0<\/b><\/span><\/span><\/span>balan\u00e7a digital de banheiro. <\/b><\/span><\/span><\/span>Para tanto, \u00e9 <\/b><\/span><\/span><\/span>necess\u00e1rio que seja posicionado os dois p\u00e9s sobre a plataforma da balan\u00e7a<\/b><\/span><\/span><\/span> e aguardar que <\/b><\/span><\/span><\/span>entre em equil\u00edbrio, <\/b><\/span><\/span><\/span>sendo, <\/b><\/span><\/span><\/span>posteriormente, exibido o valor aferido em um visor de LCD. <\/b><\/span><\/span><\/span>\"\"<\/p>\n

No <\/b><\/span><\/span><\/span>manual,<\/b><\/span><\/span><\/span> consta a <\/b><\/span><\/span><\/span>recomenda\u00e7\u00e3o:<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>\u201c N\u00e3o utilizar a balan\u00e7a em superf\u00edcies inclinadas\u201d.<\/b><\/span><\/span><\/span><\/p>\n

Que\u00a0<\/b><\/span><\/span><\/span>erros de medida podem ocorrer se esta recomenda\u00e7\u00e3o n\u00e3o for atendida?<\/b><\/span><\/span><\/span><\/p>\n

A)\u00a0<\/b><\/span><\/span><\/span>O <\/b><\/span><\/span><\/span>valor aferido ser\u00e1 menor <\/b><\/span><\/span><\/span>que o valor real, pois a <\/b><\/span><\/span><\/span>componente do peso na dire\u00e7\u00e3o paralela \u00e0 superf\u00edcie da balan\u00e7a ser\u00e1 menor, reduzindo a for\u00e7a de rea\u00e7\u00e3o da balan\u00e7a.<\/b><\/span><\/span><\/span><\/p>\n

B)\u00a0O <\/b><\/span><\/span><\/span>valor aferido ser\u00e1 menor <\/b><\/span><\/span><\/span>que o valor real, pois a <\/b><\/span><\/span><\/span>componente da for\u00e7a de rea\u00e7\u00e3o da balan\u00e7a na dire\u00e7\u00e3o paralela \u00e0 sua superf\u00edcie ser\u00e1 reduzida.<\/b><\/span><\/span><\/span><\/p>\n

C)\u00a0O <\/b><\/span><\/span><\/span>valor aferido ser\u00e1 maior <\/b><\/span><\/span><\/span>que o valor real, pois a <\/b><\/span><\/span><\/span>componente do peso na dire\u00e7\u00e3o paralela \u00e0<\/b><\/span><\/span><\/span><\/p>\n

superf\u00edcie da balan\u00e7a ser\u00e1 maior, aumentando a for\u00e7a de rea\u00e7\u00e3o da balan\u00e7a.<\/b><\/span><\/span><\/span><\/p>\n

D)\u00a0O <\/b><\/span><\/span><\/span>valor aferido ser\u00e1 menor <\/b><\/span><\/span><\/span>que o valor real, pois a <\/b><\/span><\/span><\/span>componente do peso na dire\u00e7\u00e3o perpendicular \u00e0 superf\u00edcie da balan\u00e7a ser\u00e1 menor, reduzindo a for\u00e7a de rea\u00e7\u00e3o da balan\u00e7a.<\/b><\/span><\/span><\/span><\/p>\n

E)\u00a0O <\/b><\/span><\/span><\/span>valor aferido ser\u00e1 maior <\/b><\/span><\/span><\/span>que o valor real, pois a <\/b><\/span><\/span><\/span>componente da for\u00e7a de rea\u00e7\u00e3o da balan\u00e7a na dire\u00e7\u00e3o perpendicular \u00e0 sua superf\u00edcie ser\u00e1 maior.<\/b><\/span><\/span><\/span><\/p>\n

38-(UECE-CE)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Dois cubos de\u00a0mesma densidade e tamanhos diferentes\u00a0repousam <\/b><\/span><\/span><\/span>sobre uma <\/b><\/span><\/span><\/span>mesa horizontal <\/b><\/span><\/span><\/span>e<\/b><\/span><\/span><\/span><\/p>\n

mant\u00eam contato entre si por uma de suas faces.<\/b><\/span><\/span><\/span> <\/b>\"\"<\/p>\n

A\u00a0<\/b><\/span><\/span><\/span>aresta\u00a0de\u00a0um dos cubos mede o dobro da aresta do outro. <\/b><\/span><\/span><\/span><\/p>\n

Em um <\/b><\/span><\/span><\/span>dado instante, uma for\u00e7a\u00a0constante horizontal\u00a0\"\", <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>aplicada sobre o cubo menor\u00a0<\/b><\/span><\/span><\/span>que, por sua vez,\u00a0<\/b><\/span><\/span><\/span>empurra o maior, conforme a figura.<\/b><\/span><\/span><\/span><\/p>\n

Despreze todos os atritos. <\/b><\/span><\/span><\/span>A\u00a0<\/b><\/span><\/span><\/span>raz\u00e3o entre o m\u00f3dulo de\u00a0\"\"\u00a0e o m\u00f3dulo da for\u00e7a de contato<\/b><\/span><\/span><\/span> entre os cubos \u00e9<\/b><\/span><\/span><\/span><\/p>\n

A) <\/b><\/span><\/span><\/span>8. <\/b><\/span><\/span><\/span><\/p>\n

B) <\/b><\/span><\/span><\/span>2. <\/b><\/span><\/span><\/span><\/p>\n

C) <\/b><\/span><\/span><\/span>1\/8. <\/b><\/span><\/span><\/span><\/p>\n

D) <\/b><\/span><\/span><\/span>9\/8<\/b><\/span><\/span><\/span><\/p>\n

39-(PUC-RJ)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Um\u00a0<\/b><\/span><\/span><\/span>pequeno bloco 1 de massa\u00a0m<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0= 1,0 kg\u00a0<\/b><\/span><\/span><\/span>est\u00e1 <\/b><\/span><\/span><\/span>sobre o bloco 2, comprido,<\/b><\/span><\/span><\/span> de <\/b><\/span><\/span><\/span>massa\u00a0m<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0= 0,50 kg,\u00a0<\/b><\/span><\/span><\/span>como mostrado na <\/b><\/span><\/span><\/span>figura. <\/b><\/span><\/span><\/span><\/p>\n

Ambos blocos <\/b><\/span><\/span><\/span>est\u00e3o\u00a0<\/b><\/span><\/span><\/span>inicialmente em repouso, <\/b><\/span><\/span><\/span>estando o\u00a0<\/b><\/span><\/span><\/span>bloco 1 a uma dist\u00e2ncia de 1,0 m da extremidade direita do bloco 2.<\/b><\/span><\/span><\/span><\/p>\n

Uma\u00a0<\/b><\/span><\/span><\/span>for\u00e7a horizontal \"\", constante<\/b><\/span><\/span><\/span> de\u00a0<\/b><\/span><\/span><\/span>m\u00f3dulo 13 N, <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>aplicada ao bloco 1, <\/b><\/span><\/span><\/span>que\u00a0<\/b><\/span><\/span><\/span>come\u00e7a a se mover. <\/b><\/span><\/span><\/span><\/p>\n

H\u00e1 atrito <\/b><\/span><\/span><\/span>entre as superf\u00edcies <\/b><\/span><\/span><\/span>dos blocos 1 e 2, com\u00a0coeficiente de atrito cin\u00e9tico \u03bc<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0= 0,50. <\/b><\/span><\/span><\/span><\/p>\n

Observa-se que o <\/b><\/span><\/span><\/span>bloco 2 tamb\u00e9m se movimenta. <\/b><\/span><\/span><\/span>O <\/b><\/span><\/span><\/span>coeficiente de atrito cin\u00e9tico entre o bloco 2 e o piso \u00e9 \u03bc<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0= 0,20.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Considere\u00a0g = 10 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span><\/p>\n

Resolva os seguintes itens:<\/b><\/span><\/span><\/span><\/p>\n

a)\u00a0<\/b><\/span><\/span><\/span>Fa\u00e7a os\u00a0<\/b><\/span><\/span><\/span>diagramas de for\u00e7as sobre os blocos 1 e 2.<\/b><\/span><\/span><\/span><\/p>\n

b)\u00a0<\/b><\/span><\/span><\/span>Ache a\u00a0<\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o do bloco 1,\u00a0a<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

c)\u00a0<\/b><\/span><\/span><\/span>Ache a\u00a0<\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o do bloco 2,\u00a0a<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

d)\u00a0<\/b><\/span><\/span><\/span>Calcule o\u00a0<\/b><\/span><\/span><\/span>tempo que o bloco 1 leva para chegar \u00e0 extremidade direita do bloco 2.<\/b><\/span><\/span><\/span><\/p>\n

 <\/p>\n

Confira as resolu\u00e7\u00f5es comentadas dos exerc\u00edcios<\/span><\/a><\/h3>\n","protected":false},"excerpt":{"rendered":"

APLICA\u00c7\u00d5ES DAS LEIS DE NEWTON A teoria para esses exerc\u00edcios encontra-se em fisicaevestibular.com.br – Mec\u00e2nica – nos setores: Primeira Lei de Newton, Segunda Lei de Newton, Terceira Lei de Newton, Tipos de For\u00e7as, Peso e Massa, Polias e Roldanas, Aplica\u00e7\u00f5es das Leis de Newton para corpos apoiados ou suspensos e For\u00e7as no Movimento Circular. Exerc\u00edcios de vestibulares com resolu\u00e7\u00f5es comentadas<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2508,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"class_list":["post-2541","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2541","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/comments?post=2541"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2541\/revisions"}],"predecessor-version":[{"id":2547,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2541\/revisions\/2547"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2508"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=2541"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}