{"id":3943,"date":"2018-04-30T19:33:00","date_gmt":"2018-04-30T19:33:00","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=3943"},"modified":"2024-09-04T12:27:54","modified_gmt":"2024-09-04T12:27:54","slug":"resolucao-comentada-das-questoes-de-fisica-da-escola-naval-20182017","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/universidades-2018\/escola-naval-20182017\/resolucao-comentada-das-questoes-de-fisica-da-escola-naval-20182017\/","title":{"rendered":"Resolu\u00e7\u00e3o comentada das quest\u00f5es de F\u00cdSICA da Escola Naval \u2013 2018\/2017"},"content":{"rendered":"

Resolu\u00e7\u00e3o comentada das quest\u00f5es de F\u00cdSICA da <\/span><\/span><\/span><\/p>\n

Escola Naval \u2013 2018\/2017<\/span><\/span><\/span><\/p>\n

01- <\/span><\/span><\/span><\/p>\n

Fragata Independ\u00eancia<\/b><\/span><\/span><\/span><\/p>\n

Ela se <\/b><\/span><\/span><\/span>desloca <\/b><\/span><\/span><\/span>para o <\/b><\/span><\/span><\/span>norte<\/b><\/span><\/span><\/span> com <\/b><\/span><\/span><\/span>velocidade de V<\/b><\/span><\/span><\/span>I<\/b><\/span><\/span><\/sub><\/span> = 15\u221a2 n\u00f3s <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>correnteza tem na dire\u00e7\u00e3o norte-sul<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

e <\/b><\/span><\/span><\/span>velocidade de 2 n\u00f3s. <\/b><\/span><\/span><\/span><\/p>\n

Assim a <\/b><\/span><\/span><\/span>velocidade relativa da fragata Independ\u00eancia em rela\u00e7\u00e3o ao farol <\/b><\/span><\/span><\/span>(vista por uma pessoa no farol) ser\u00e1 <\/b><\/span><\/span><\/span>V<\/b><\/span><\/span><\/span>RI<\/b><\/span><\/span><\/sub><\/span> = (15\u221a2 \u2013 2) n\u00f3s, <\/b><\/span><\/span><\/span>no <\/b><\/span><\/span><\/span>sentido sul-norte.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Fragata Rademaker<\/b><\/span><\/span><\/span><\/p>\n

Na <\/b><\/span><\/span><\/span>sequ\u00eancia abaixo, <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>\u00e2ngulo entre o nordeste e o norte e o leste \u00e9 de 45<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span> <\/b>e assim, voc\u00ea <\/b><\/span><\/span><\/span>decomp\u00f5e<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>velocidade V<\/b><\/span><\/span><\/span>R<\/b><\/span><\/span><\/sub><\/span> = 20\u221a2 n\u00f3s <\/b><\/span><\/span><\/span>em sua <\/b><\/span><\/span><\/span>parcelas vertical e horizontal, <\/b><\/span><\/span><\/span>cada uma de <\/b><\/span><\/span><\/span>intensidade V<\/b><\/span><\/span><\/span>v<\/b><\/span><\/span><\/sub><\/span> = V<\/b><\/span><\/span><\/span>h<\/b><\/span><\/span><\/sub><\/span> \"\"<\/b><\/span><\/span><\/span><\/p>\n

V<\/b><\/span><\/span><\/span>R<\/b><\/span><\/span><\/sub><\/span>.cos45<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span> = 20.\"\" \"\" <\/b><\/span><\/span><\/span>V<\/b><\/span><\/span><\/span>v<\/b><\/span><\/span><\/sub><\/span> = V<\/b><\/span><\/span><\/span>h<\/b><\/span><\/span><\/sub><\/span> = 10\"\" n\u00f3s.<\/b><\/span><\/span><\/span><\/p>\n

Em seguida, <\/b><\/span><\/span><\/span>considerando <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>velocidade relativa apenas na vertical, <\/b><\/span><\/span><\/span>onde voc\u00ea tem <\/b><\/span><\/span><\/span>V<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span> = 2 n\u00f3s (sul), <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>parcela V<\/b><\/span><\/span><\/span>v<\/b><\/span><\/span><\/sub><\/span> dever\u00e1 ter intensidade V<\/b><\/span><\/span><\/span>v <\/b><\/span><\/span><\/sub><\/span>= (10\u221a2 \u2013 2) n\u00f3s (norte).<\/b><\/span><\/span><\/span><\/p>\n

Ent\u00e3o, a <\/b><\/span><\/span><\/span>fragata Rademaker <\/b><\/span><\/span><\/span>se desloca <\/b><\/span><\/span><\/span>ao mesmo tempo com velocidades de dire\u00e7\u00e3o e sentidos <\/b><\/span><\/span><\/span>indicados na <\/b><\/span><\/span><\/span>\u00faltima figura acima.<\/b><\/span><\/span><\/span><\/p>\n

C\u00e1lculo do <\/b><\/span><\/span><\/span>m\u00f3dulo da velocidade relativa <\/b><\/span><\/span><\/span>da <\/b><\/span><\/span><\/span>Fragata Independ\u00eancia<\/b><\/span><\/span><\/span>, em n\u00f3s, em <\/b><\/span><\/span><\/span>rela\u00e7\u00e3o \u00e0 Fragata Rademaker, analisando a sequ\u00eancia <\/b><\/span><\/span><\/span>de figuras abaixo:<\/b><\/span><\/span><\/span><\/p>\n

Na <\/b><\/span><\/span><\/span>figura I<\/b><\/span><\/span><\/span> voc\u00ea tem <\/b><\/span><\/span><\/span>a velocidade resultante horizontal e vertical final de cada fragata,<\/b><\/span><\/span><\/span> vistas por um observador no farol. Na <\/b><\/span><\/span><\/span>figura II s\u00f3 as componentes verticais <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>cada uma<\/b><\/span><\/span><\/span> e, como elas se <\/b><\/span><\/span><\/span>movem<\/b><\/span><\/span><\/span> <\/b>no mesmo sentido a velocidade relativa final V\u2019<\/b><\/span><\/span><\/span>v<\/b><\/span><\/span><\/sub><\/span> <\/b>na <\/b><\/span><\/span><\/span>dire\u00e7\u00e3o vertical <\/b><\/span><\/span><\/span>ser\u00e1 a <\/b><\/span><\/span><\/span>diferen\u00e7a entre <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

essas velocidades \"\"<\/b><\/span><\/span><\/span> <\/b>V\u2019<\/b><\/span><\/span><\/span>v<\/b><\/span><\/span><\/sub><\/span> <\/b>= (15\u221a2 \u2013 2) \u2013 (10\u221a2 \u2013 2) = 15\u221a2 \u2013 2 \u2013 10\u221a2 + 2 \"\" <\/b><\/span><\/span><\/span>V\u2019<\/b><\/span><\/span><\/span>v<\/b><\/span><\/span><\/sub><\/span> = 5\u221a2 n\u00f3s<\/b><\/span><\/span><\/span>.(figura III). <\/b><\/span><\/span><\/span><\/p>\n

Na <\/b><\/span><\/span><\/span>dire\u00e7\u00e3o horizontal <\/b><\/span><\/span><\/span>a velocidade \u00e9 <\/b><\/span><\/span><\/span>apenas a da fragata Rademaker <\/b><\/span><\/span><\/span>de sentido oeste-leste e <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

intensidade <\/b><\/span><\/span><\/span>V\u2019<\/b><\/span><\/span><\/span>h<\/b><\/span><\/span><\/sub><\/span> = 10<\/b><\/span><\/span><\/span>\u221a2 n\u00f3s.<\/b><\/span><\/span><\/span><\/p>\n

Para o <\/b><\/span><\/span><\/span>c\u00e1lculo do m\u00f3dulo da velocidade relativa pedida <\/b><\/span><\/span><\/span>voc\u00ea deve aplicar <\/b><\/span><\/span><\/span>Pit\u00e1goras<\/b><\/span><\/span><\/span> na <\/b><\/span><\/span><\/span>soma<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

vetorial <\/b><\/span><\/span><\/span>acima \"\" <\/b><\/span><\/span><\/span>V\u2019<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span> =<\/b><\/span><\/span><\/span> (5\u221a2)<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span> + (10\u221a2)<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span> = 25.2 + 100.2 = 50 + 200 \"\" <\/b><\/span><\/span><\/span>V\u2019<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span> =<\/b><\/span><\/span><\/span> \u221a250 <\/b><\/span><\/span><\/span>= 15,81 n\u00f3s.<\/b><\/span><\/span><\/span><\/p>\n

R- D<\/b><\/span><\/span><\/span><\/p>\n

02- <\/span><\/span><\/span>Colocando as for\u00e7as <\/b><\/span><\/span><\/span>que agem sobre o <\/b><\/span><\/span><\/span>sistema<\/b><\/span><\/span><\/span> e <\/b><\/span><\/span><\/span>calculando<\/b><\/span><\/span><\/span> o <\/b><\/span><\/span><\/span>momento de cada for\u00e7a <\/b><\/span><\/span><\/span>com o<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

polo em O<\/b><\/span><\/span><\/span>, sendo dados \"\" <\/b><\/span><\/span><\/span>T =<\/b><\/span><\/span><\/span> 15\u221a2 N; <\/b><\/span><\/span><\/span>P<\/b><\/span><\/span><\/span>bloco<\/b><\/span><\/span><\/sub><\/span> = mg = 2.10 <\/b><\/span><\/span><\/span>= 20 N<\/b><\/span><\/span><\/span>; <\/b><\/span><\/span><\/span>L = <\/b><\/span><\/span><\/span>5,0 m; peso da barra <\/b><\/span><\/span><\/span>P<\/b><\/span><\/span><\/span>barra<\/b><\/span><\/span><\/sub><\/span> e estabelecendo o <\/b><\/span><\/span><\/span>sentido hor\u00e1rio de rota\u00e7\u00e3o em torno de O como positivo <\/b><\/span><\/span><\/span>e lembrando que <\/b><\/span><\/span><\/span>d \u00e9 a dist\u00e2ncia entre o prolongamento da for\u00e7a e o polo:<\/b><\/span><\/span><\/span><\/p>\n

\"\" Momento da for\u00e7a peso do bloco<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\" <\/span>Momento da for\u00e7a de tra\u00e7\u00e3o<\/b><\/span><\/span><\/span><\/p>\n

\"\"\"\" Momento da for\u00e7a peso da barra<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\" Momento da for\u00e7a normal<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

R- C<\/b><\/span><\/span><\/span><\/p>\n

03- <\/b><\/span><\/span><\/span>Como <\/b><\/span><\/span><\/span>n\u00e3o pode haver escorregamento<\/b><\/span><\/span><\/span> entre o <\/b><\/span><\/span><\/span>bloco e a plataforma <\/b><\/span><\/span><\/span>voc\u00ea deve <\/b><\/span><\/span><\/span>utilizar<\/b><\/span><\/span><\/span> o <\/b><\/span><\/span><\/span>coeficiente de atrito est\u00e1tico m\u00e1ximo \"\"<\/b><\/span><\/span><\/span>e<\/b><\/span><\/span><\/sub><\/span> <\/b>(bloco e plataforma est\u00e3o em contato, mas n\u00e3o deslizam, est\u00e3o na imin\u00eancia de deslizar)<\/b><\/span><\/span><\/span><\/p>\n

Massa do bloco \"\"<\/b><\/span><\/span><\/span> <\/b>m<\/b><\/span><\/span><\/span>b<\/b><\/span><\/span><\/sub><\/span> =<\/b><\/span><\/span><\/span> 12 kg \"\" <\/b><\/span><\/span><\/span>massa da plataforma \"\"<\/b><\/span><\/span><\/span> <\/b>m<\/b><\/span><\/span><\/span>p<\/b><\/span><\/span><\/sub><\/span> = <\/b><\/span><\/span><\/span>3 kg \"\" \"\"<\/b><\/span><\/span><\/span>e<\/b><\/span><\/span><\/sub><\/span> = 0,3<\/b><\/span><\/span><\/span><\/p>\n

Observe que <\/b><\/span><\/span><\/span>bloco e plataforma constituem um \u00fanico sistema <\/b><\/span><\/span><\/span>sujeito a uma <\/b><\/span><\/span><\/span>for\u00e7a de intensidade F<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>horizontal e para a direita, <\/b><\/span><\/span><\/span>fazendo com que esse <\/b><\/span><\/span><\/span>sistema se mova para a direita, pois a superf\u00edcie horizontal em que est\u00e1 apoiada n\u00e3o oferece atrito.<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>for\u00e7a <\/b><\/span><\/span><\/span>que age sobre o <\/b><\/span><\/span><\/span>sistema (bloco + plataforma)<\/b><\/span><\/span><\/span> provoca uma <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o de intensidade <\/b><\/span><\/span><\/span>a<\/b><\/span><\/span><\/span> <\/b>tal<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Como o <\/b><\/span><\/span><\/span>bloco (e todo o sistema) <\/b><\/span><\/span><\/span>se <\/b><\/span><\/span><\/span>move <\/b><\/span><\/span><\/span>para a <\/b><\/span><\/span><\/span>direita<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>for\u00e7a resultante <\/b><\/span><\/span><\/span>sobre ele ter\u00e1 <\/b><\/span><\/span><\/span>intensidade<\/b><\/span><\/span><\/span> <\/b>F<\/b><\/span><\/span><\/span>R <\/b><\/span><\/span><\/sub><\/span>= m<\/b><\/span><\/span><\/span>bloco<\/b><\/span><\/span><\/sub><\/span>.a, horizontal e para a direita.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

04- <\/b><\/span><\/span><\/span>Veja nas <\/b><\/span><\/span><\/span>figuras abaixo<\/b><\/span><\/span><\/span> que, como \u00e9 pedido o <\/b><\/span><\/span><\/span>m\u00f3dulo da for\u00e7a el\u00e9trica resultante (F\u2019) em Q<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sub><\/span>, o <\/b><\/span><\/span><\/span>sinal de Q<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sub><\/span> n\u00e3o influi na resolu\u00e7\u00e3o<\/b><\/span><\/span><\/span> j\u00e1 que seu <\/b><\/span><\/span><\/span>m\u00f3dulo e dire\u00e7\u00e3o s\u00e3o os mesmos, <\/b><\/span><\/span><\/span>mudando<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

apenas o sentido que depende do sinal de Q<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sub><\/span> (leste ou oeste).<\/b><\/span><\/span><\/span><\/p>\n

Vamos ent\u00e3o <\/b><\/span><\/span><\/span>considerar o caso em que Q<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sub><\/span> \u00e9 positiva<\/b><\/span><\/span><\/span> e, nessas condi\u00e7\u00f5es <\/b><\/span><\/span><\/span>resolver utilizando apenas os m\u00f3dulos <\/b><\/span><\/span><\/span>(j\u00e1 que os sinais n\u00e3o influem) considerando <\/b><\/span><\/span><\/span>d = D\/2 = 2\/2 = 1 m; Q<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span> = Q<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span> = Q<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sub><\/span> <\/b><\/p>\n

\"\"<\/p>\n

= q<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span> e kq<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>2 <\/b><\/span><\/span><\/sup><\/span>= 10 N.m<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

C\u00e1lculo da <\/b><\/span><\/span><\/span>dist\u00e2ncia d\u2019<\/b><\/span><\/span><\/span> entre as <\/b><\/span><\/span><\/span>duas cargas q<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span> <\/b>aplicando <\/b><\/span><\/span><\/span>Pit\u00e1goras<\/b><\/span><\/span><\/span> no <\/b><\/span><\/span><\/span>tri\u00e2ngulo ret\u00e2ngulo <\/b><\/span><\/span><\/span>na <\/b><\/span><\/span><\/span>figura acima.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Decompondo cada F <\/b><\/span><\/span><\/span>em suas <\/b><\/span><\/span><\/span>parcelas F<\/b><\/span><\/span><\/span>x<\/b><\/span><\/span><\/sub><\/span> e F<\/b><\/span><\/span><\/span>y<\/b><\/span><\/span><\/sub><\/span>, <\/b><\/span><\/span><\/span>na <\/b><\/span><\/span><\/span>vertical elas se anulam<\/b><\/span><\/span><\/span>, pois possuem o <\/b><\/span><\/span><\/span>mesmo m\u00f3dulo (F<\/b><\/span><\/span><\/span>y<\/b><\/span><\/span><\/sub><\/span> = Fsen\"\".<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

R- B<\/b><\/span><\/span><\/span><\/p>\n

05- <\/b><\/span><\/span><\/span><\/p>\n

For\u00e7a eletromotriz induzida pelo movimento<\/b><\/span><\/span><\/span><\/p>\n

For\u00e7a eletromotriz gerada por um condutor m\u00f3vel num campo el\u00e9trico uniforme<\/b><\/span><\/span><\/span><\/p>\n

For\u00e7a eletromotriz\u00a0\u03b5<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>gerada por um\u00a0<\/b><\/span><\/span><\/span>condutor m\u00f3vel imerso num campo el\u00e9trico uniforme\u00a0\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 esse\u00a0<\/b><\/span><\/span><\/span>condutor tem o comportamento de um gerador mec\u00e2nico de eletricidade de fem\u00a0\u03b5.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

S\u00e3o fornecidos: <\/b><\/span><\/span><\/span>m\u00f3dulo do campo magn\u00e9tico <\/b><\/span><\/span><\/span>B = 6,0 T<\/b><\/span><\/span><\/span>; comprimento da barra condutora <\/b><\/span><\/span><\/span>L = 1,0 m <\/b><\/span><\/span><\/span>e<\/b><\/span><\/span><\/span> <\/b>velocidade<\/b><\/span><\/span><\/span> de deslocamento da barra condutora <\/b><\/span><\/span><\/span>v = 2 m\/s. <\/b><\/span><\/span><\/span><\/p>\n

C\u00e1lculo da <\/b><\/span><\/span><\/span>for\u00e7a eletromotriz induzida (\"\") <\/b><\/span><\/span><\/span>na barra condutora pela express\u00e3o \"\"<\/b><\/span><\/span><\/span> = B.L.v <\/b><\/span><\/span><\/span>= 6.1.2 \"\" <\/b><\/span><\/span><\/span><\/p>\n

\"\"= 12 V.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Estando a <\/b><\/span><\/span><\/span>barra descendo com velocidade constante<\/b><\/span><\/span><\/span> (equil\u00edbrio din\u00e2mico \u201cfor\u00e7a resultante nula\u201d) ent\u00e3o <\/b><\/span><\/span><\/span>deve surgir sobre ela uma for\u00e7a magn\u00e9tica de intensidade F<\/b><\/span><\/span><\/span>m<\/b><\/span><\/span><\/sub><\/span> <\/b>(vertical e para cima) que deve <\/b><\/span><\/span><\/span>anular a for\u00e7a externa de intensidade F <\/b><\/span><\/span><\/span>(vertical e para baixo).<\/b><\/span><\/span><\/span><\/p>\n

Essa <\/b><\/span><\/span><\/span>for\u00e7a magn\u00e9tica tem as seguintes caracter\u00edsticas:<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

No <\/b><\/span><\/span><\/span>caso do exerc\u00edcio <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>for\u00e7a magn\u00e9tica tem dire\u00e7\u00e3o vertical e sentido para cima <\/b><\/span><\/span><\/span>(figura abaixo).<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0C\u00e1lculo da <\/b><\/span><\/span><\/span>intensidade da for\u00e7a magn\u00e9tica<\/b><\/span><\/span><\/span> pela express\u00e3o <\/b><\/span><\/span><\/span>F<\/b><\/span><\/span><\/span>m<\/b><\/span><\/span><\/sub><\/span> = B.i.L.sen\"\"<\/b><\/span><\/span><\/span>sendo dados: <\/b><\/span><\/span><\/span>B =<\/b><\/span><\/span><\/span> 6 T; <\/b><\/span><\/span><\/span>i =<\/b><\/span><\/span><\/span> 12 A; <\/b><\/span><\/span><\/span>L =<\/b><\/span><\/span><\/span> 1 m e \"\"<\/b><\/span><\/span><\/span> = 90<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>:<\/b><\/span><\/span><\/span><\/p>\n

F<\/b><\/span><\/span><\/span>m<\/b><\/span><\/span><\/sub><\/span> =<\/b><\/span><\/span><\/span> 6.12.1.1 \"\" <\/b><\/span><\/span><\/span>F<\/b><\/span><\/span><\/span>m<\/b><\/span><\/span><\/sub><\/span> = 72 N.<\/b><\/span><\/span><\/span><\/p>\n

R – E<\/b><\/span><\/span><\/span><\/p>\n

06- <\/b><\/span><\/span><\/span>Trecho AB<\/b><\/span><\/span><\/span> \"\" trata-se de uma <\/b><\/span><\/span><\/span>expans\u00e3o<\/b><\/span><\/span><\/span> (volume aumentando) <\/b><\/span><\/span><\/span>isot\u00e9rmica <\/b><\/span><\/span><\/span>(ocorre \u00e0 temperatura T constante T<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span> = T<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>).<\/b><\/span><\/span><\/span><\/p>\n

Trecho BC \"\"<\/b><\/span><\/span><\/span> trata-se de um <\/b><\/span><\/span><\/span>aquecimento T<\/b><\/span><\/span><\/span>C<\/b><\/span><\/span><\/sub><\/span> > T<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span> <\/b>(a isoterma que passa por C est\u00e1 mais afastada da origem que a isoterma que passa por B) <\/b><\/span><\/span><\/span>isovolum\u00e9trico <\/b><\/span><\/span><\/span>(isoc\u00f3rico ou isom\u00e9trico) a <\/b><\/span><\/span><\/span>volume constante.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Trecho CA \"\"<\/b><\/span><\/span><\/span> trata-se de uma <\/b><\/span><\/span><\/span>compress\u00e3o <\/b><\/span><\/span><\/span>(volume diminuindo) junto com um <\/b><\/span><\/span><\/span>resfriamento T<\/b><\/span><\/span><\/span>C<\/b><\/span><\/span><\/sub><\/span> > T<\/b><\/span><\/span><\/span>A <\/b><\/span><\/span><\/sub><\/span>(a isoterma que passa por C est\u00e1 mais afastada da origem que a isoterma que passa por A) <\/b><\/span><\/span><\/span>isob\u00e1rica (press\u00e3o constante). <\/b><\/span><\/span><\/span><\/p>\n

R – A<\/b><\/span><\/span><\/span><\/p>\n

07- <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

08- <\/b><\/span><\/span><\/span>Tipicamente o <\/b><\/span><\/span><\/span>bin\u00e1rio de estrelas <\/b><\/span><\/span><\/span>\u00e9 um <\/b><\/span><\/span><\/span>sistema isolado n\u00e3o sujeito \u00e0 a\u00e7\u00e3o de for\u00e7as externas, <\/b><\/span><\/span><\/span>mantido <\/b><\/span><\/span><\/span>exclusivamente pela a\u00e7\u00e3o da for\u00e7a de intera\u00e7\u00e3o gravitacional entre ambos os corpos (lei da Gravita\u00e7\u00e3o Universal) .<\/b><\/span><\/span><\/span><\/p>\n

Express\u00e3o matem\u00e1tica da lei da Gravita\u00e7\u00e3o Universal<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Pelo enunciado o <\/b><\/span><\/span><\/span>per\u00edodo de rota\u00e7\u00e3o (T) \u00e9 constante <\/b><\/span><\/span><\/span>o que implica que a <\/b><\/span><\/span><\/span>velocidade angular<\/b><\/span><\/span><\/span> <\/b>(W = 2\u03c0\/T) <\/b><\/span><\/span><\/span>tamb\u00e9m \u00e9 constante, <\/b><\/span><\/span><\/span>pois todas as grandezas dessa equa\u00e7\u00e3o <\/b><\/span><\/span><\/span>s\u00e3o constantes. <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Assim, a <\/b><\/span><\/span><\/span>energia cin\u00e9tica de cada estrela <\/b><\/span><\/span><\/span>(e do sistema) tamb\u00e9m \u00e9 <\/b><\/span><\/span><\/span>constante <\/b><\/span><\/span><\/span>e ser\u00e1 conservada o que pode ser provado pela <\/b><\/span><\/span><\/span>express\u00e3o da energia cin\u00e9tica (E<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span> = M.V<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\/2), sendo M e V constantes.<\/b><\/span><\/span><\/span><\/p>\n

R- B<\/b><\/span><\/span><\/span><\/p>\n

09- <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

R- B<\/b><\/span><\/span><\/span><\/p>\n

10- <\/b><\/span><\/span><\/span>Observe que, quando o enunciado <\/b><\/span><\/span><\/span>afirma que a pot\u00eancia fornecida nessa transforma\u00e7\u00e3o foi de P = 360 cal\/s, <\/b><\/span><\/span><\/span>ele est\u00e1 <\/b><\/span><\/span><\/span>informando que uma fonte est\u00e1 fornecendo Q = 360 calorias em cada segundo durante toda a transforma\u00e7\u00e3o.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Vamos agora <\/b><\/span><\/span><\/span>calcular <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>calor espec\u00edfico no estado l\u00edquido <\/b><\/span><\/span><\/span>j\u00e1 que no <\/b><\/span><\/span><\/span>estado s\u00f3lido n\u00e3o \u00e9 poss\u00edvel, <\/b><\/span><\/span><\/span>pois o <\/b><\/span><\/span><\/span>gr\u00e1fico n\u00e3o fornece <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>temperatura inicial em que come\u00e7a a transforma\u00e7\u00e3o.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

R- C<\/b><\/span><\/span><\/span><\/p>\n

11- <\/b><\/span><\/span><\/span>A\u00a0<\/b><\/span><\/span><\/span>densidade linear\u00a0<\/b><\/span><\/span><\/span>da\u00a0<\/b><\/span><\/span><\/span>primeira corda (\u00b5<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>)<\/b><\/span><\/span><\/span>\u00a0\u00e9\u00a0<\/b><\/span><\/span><\/span>maior do que a da segunda (\u00b5<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>)<\/b><\/span><\/span><\/span>, ou seja,\u00a0<\/b><\/span><\/span><\/span>\u00b5<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0>\u00a0\u00b5<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

Quando o\u00a0<\/b><\/span><\/span><\/span>pulso chega ao ponto de jun\u00e7\u00e3o das cordas,\u00a0<\/b><\/span><\/span><\/span>ocorre ao\u00a0<\/b><\/span><\/span><\/span>mesmo tempo refra\u00e7\u00e3o e reflex\u00e3o. Esse ponto (jun\u00e7\u00e3o) funciona\u00a0<\/b><\/span><\/span><\/span>como uma <\/b><\/span><\/span><\/span>extremidade livre\u00a0\u00a0<\/b><\/span><\/span><\/span>e o\u00a0<\/b><\/span><\/span><\/span>pulso refletido retorna sem invers\u00e3o de fase.<\/b><\/span><\/span><\/span><\/p>\n

O\u00a0<\/b><\/span><\/span><\/span>pulso refratado\u00a0<\/b><\/span><\/span><\/span>tem sempre a\u00a0<\/b><\/span><\/span><\/span>mesma fase do incidente.<\/b><\/span><\/span><\/span><\/p>\n

Parte da energia do pulso incidente\u00a0<\/b><\/span><\/span><\/span>\u00e9\u00a0<\/b><\/span><\/span><\/span>transmitida ao pulso refratado\u00a0<\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>parte ao pulso refletido<\/b><\/span><\/span><\/span>,\u00a0<\/b><\/span><\/span><\/span>diminuindo<\/b><\/span><\/span><\/span>\u00a0assim a\u00a0<\/b><\/span><\/span><\/span>amplitude desses dois pulsos<\/b><\/span><\/span><\/span>, ou seja,\u00a0<\/b><\/span><\/span><\/span>A > A<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0e A > A<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A\u00a0<\/b><\/span><\/span><\/span>for\u00e7a de tra\u00e7\u00e3o (T)\u00a0<\/b><\/span><\/span><\/span>nas\u00a0<\/b><\/span><\/span><\/span>duas cordas \u00e9 a mesma\u00a0<\/b><\/span><\/span><\/span>e a\u00a0<\/b><\/span><\/span><\/span>velocidade em cada corda \u00e9 fornecida<\/b><\/span><\/span><\/span>\u00a0por<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Observe\u00a0<\/b><\/span><\/span><\/span>na express\u00e3o acima\u00a0<\/b><\/span><\/span><\/span>que a\u00a0<\/b><\/span><\/span><\/span>velocidade V \u00e9 inversamente proporcional \u00e0 densidade linear\u00a0\u00b5,\u00a0<\/b><\/span><\/span><\/span>assim, a\u00a0<\/b><\/span><\/span><\/span>velocidade da onda na corda mais densa\u00a0<\/b><\/span><\/span><\/span>\u201cmais pesada\u201d\u00a0<\/b><\/span><\/span><\/span>\u00e9 menor do que a velocidade na corda menos densa\u00a0<\/b><\/span><\/span><\/span>\u201cmais leve\u201d<\/b><\/span><\/span><\/span>. Ent\u00e3o,\u00a0V<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0> V<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

A\u00a0<\/b><\/span><\/span><\/span>frequ\u00eancia f<\/b><\/span><\/span><\/span>\u00a0\u00e9 a\u00a0<\/b><\/span><\/span><\/span>mesma nas duas cordas,\u00a0<\/b><\/span><\/span><\/span>pois a<\/b><\/span><\/span><\/span>\u00a0fonte \u00e9 a mesma.<\/b><\/span><\/span><\/span><\/p>\n

V = \u03bbf\u00a0\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0\u00a0<\/b><\/span><\/span><\/span>f = V\/\u03bb\u00a0\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 f = V<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\/\u03bb<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0e f = V<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\/\u03bb<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0\"\"\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span>V<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\/\u03bb<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>= V<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\/\u03bb<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0(I)<\/b><\/span><\/span><\/span><\/p>\n

Observe na\u00a0<\/b><\/span><\/span><\/span>express\u00e3o (I)\u00a0<\/b><\/span><\/span><\/span>que,\u00a0<\/b><\/span><\/span><\/span>quanto maior a velocidade V maior o comprimento de onda\u00a0\u03bb.\u00a0<\/b><\/span><\/span><\/span>Portanto o\u00a0<\/b><\/span><\/span><\/span>comprimento de onda da corda menos densa \u00e9 maior que o da corda mais densa.<\/b><\/span><\/span><\/span><\/p>\n

R – B\u00a0<\/b><\/span><\/span><\/span><\/p>\n

12-<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Como o amper\u00edmetro ideal indica corrente el\u00e9trica nula na pilha (gerador) 2, nele, i = 0,\u00a0<\/b><\/span><\/span>ou seja, o\u00a0<\/b><\/span><\/span>gerador est\u00e1 em\u00a0circuito aberto,\u00a0portanto voc\u00ea tem a situa\u00e7\u00e3o da figura baixo:<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Assim, a <\/b><\/span><\/span><\/span>tens\u00e3o (ddp, voltagem \u201cU\u201d) <\/b><\/span><\/span><\/span>nos <\/b><\/span><\/span><\/span>terminais da l\u00e2mpada <\/b><\/span><\/span><\/span>de resist\u00eancia <\/b><\/span><\/span><\/span>R<\/b><\/span><\/span><\/span>L<\/b><\/span><\/span><\/sub><\/span> ser\u00e1 a pr\u00f3pria <\/b><\/span><\/span><\/span>for\u00e7a eletromotriz da pilha 2 (\"\"), ou seja, U = \"\".<\/b><\/span><\/span><\/span><\/p>\n

Ent\u00e3o o <\/b><\/span><\/span><\/span>circuito ficar\u00e1 conforme o indicado nas figuras abaixo onde<\/b><\/span><\/span><\/span>, na sequ\u00eancia, \u00e9 calculada <\/b><\/span><\/span><\/span>a resist\u00eancia equivalente:<\/b><\/span><\/span><\/span><\/p>\n

\"\"R<\/b><\/span><\/span><\/span>eq<\/b><\/span><\/span><\/sub><\/span> = U(\"\"<\/b><\/span><\/span><\/span>)\/i \"\"<\/b><\/span><\/span><\/span> 1 = 1,5\/i \"\" <\/b><\/span><\/span><\/span>i = 1,5 A.<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>ddp pedida na l\u00e2mpada de resist\u00eancia R<\/b><\/span><\/span><\/span>L<\/b><\/span><\/span><\/sub><\/span> = 2\/3 \u2126 ser\u00e1 \"\"<\/b><\/span><\/span><\/span> <\/b>R<\/b><\/span><\/span><\/span>L<\/b><\/span><\/span><\/sub><\/span> = U\/i \"\"<\/b><\/span><\/span><\/span> 2\/3 = U<\/b><\/span><\/span><\/span>L<\/b><\/span><\/span><\/sub><\/span>\/1,5 \"\" U<\/b><\/span><\/span><\/span>L<\/b><\/span><\/span><\/sub><\/span> = 3\/3 \"\" <\/b><\/span><\/span><\/span>U<\/b><\/span><\/span><\/span>L<\/b><\/span><\/span><\/sub><\/span>= 1 V<\/b><\/span><\/span><\/span><\/p>\n

R- D<\/b><\/span><\/span><\/span><\/p>\n

 <\/p>\n

Voltar para os exerc\u00edcios<\/span><\/a><\/h3>\n","protected":false},"excerpt":{"rendered":"

Resolu\u00e7\u00e3o comentada das quest\u00f5es de F\u00cdSICA da Escola Naval \u2013 2018\/2017 01- Fragata Independ\u00eancia Ela se desloca para o norte com velocidade de VI = 15\u221a2 n\u00f3s e a correnteza tem na dire\u00e7\u00e3o norte-sul e velocidade de 2 n\u00f3s. Assim a velocidade relativa da fragata Independ\u00eancia em rela\u00e7\u00e3o ao farol (vista por uma pessoa no farol) ser\u00e1 VRI = (15\u221a2<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":3941,"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-3943","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3943","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=3943"}],"version-history":[{"count":1,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3943\/revisions"}],"predecessor-version":[{"id":3944,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3943\/revisions\/3944"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3941"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=3943"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}