{"id":299,"date":"2014-12-17T13:55:48","date_gmt":"2014-12-17T13:55:48","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=299"},"modified":"2024-09-02T16:59:57","modified_gmt":"2024-09-02T16:59:57","slug":"exercicios-da-unb-2015","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/universidades-2015\/exercicios-da-unb-2015\/","title":{"rendered":"Exerc\u00edcios da UnB 2015"},"content":{"rendered":"

UnB-015<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A\u00a0<\/b><\/span><\/span><\/span>Universidade de Bras\u00edlia (UnB)\u00a0<\/b><\/span><\/span><\/span>\u00e9 uma\u00a0universidade\u00a0p\u00fablica\u00a0brasileira, com sede na <\/b><\/span><\/span><\/span>cidade de\u00a0Bras\u00edlia, no\u00a0Distrito Federal\u00a0e com Campus nas cidades de Bras\u00edlia, Planaltina,\u00a0Gama,\u00a0Ceil\u00e2ndia\u00a0e\u00a0Parano\u00e1\u00a0(em projeto). <\/b><\/span><\/span><\/span>\u00c9 a <\/b><\/span><\/span><\/span>maior institui\u00e7\u00e3o de ensino <\/b><\/span><\/span><\/span>superior do\u00a0centro-oeste\u00a0do\u00a0Brasil\u00a0e uma das <\/b><\/span><\/span><\/span>mais importantes do pa\u00eds<\/b><\/span><\/span><\/span>. Foi avaliada pelo\u00a0MEC\u00a0atrav\u00e9s do\u00a0\u00cdndice Geral de Cursos\u00a0como a <\/b><\/span><\/span><\/span>melhor universidade da regi\u00e3o Centro-Oeste, seguida pela\u00a0UFG\u00a0e\u00a0UFGD.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A figura abaixo ilustra, de forma esquematizada, um sistema de <\/b><\/span><\/span><\/span>transmiss\u00e3o coroa-catraca <\/b><\/span><\/span><\/span>de uma<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

bicicleta<\/b><\/span><\/span><\/span>. Na figura, <\/b><\/span><\/span><\/span>r<\/b><\/span><\/span><\/span>a<\/b><\/span><\/span><\/sub><\/span>, r<\/b><\/span><\/span><\/span>b<\/b><\/span><\/span><\/sub><\/span>, r<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span> e\u03c9<\/b><\/span><\/span><\/span>a<\/b><\/span><\/span><\/sub><\/span>, \u03c9<\/b><\/span><\/span><\/span>b<\/b><\/span><\/span><\/sub><\/span>, \u03c9<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span>identificam, respectivamente, os <\/b><\/span><\/span><\/span>raios e as velocidades angulares da coroa, da catraca e da roda da bicicleta. <\/b><\/span><\/span><\/span>Considere a situa\u00e7\u00e3o em que um ciclista, pedalando em um modelo de bicicleta com <\/b><\/span><\/span><\/span>r<\/b><\/span><\/span><\/span>a<\/b><\/span><\/span><\/sub><\/span> = 10 cm, r<\/b><\/span><\/span><\/span>b<\/b><\/span><\/span><\/sub><\/span> = 5 cm e r<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span> = 40 cm<\/b><\/span><\/span><\/span>, mantem <\/b><\/span><\/span><\/span>velocidade constante<\/b><\/span><\/span><\/span>em bicicleta cujo <\/b><\/span><\/span><\/span>pedal leva 0,1 segundo <\/b><\/span><\/span><\/span>para ser deslocado da <\/b><\/span><\/span><\/span>posi\u00e7\u00e3o 1 para a posi\u00e7\u00e3o <\/b><\/span><\/span><\/span>2, na horizontal. <\/b><\/span><\/span><\/span>Considere, ainda, que a bicicleta <\/b><\/span><\/span><\/span>n\u00e3o sofre deslizamentos<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

Tendo como referencia as informa\u00e7\u00f5es acima<\/b><\/span><\/span><\/span>, julgue os itens 01 e 02<\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>fa\u00e7a o que se pede no item 03.<\/b><\/span><\/span><\/span><\/p>\n

01-(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Se o <\/b><\/span><\/span><\/span>per\u00edodo do movimento da roda \u00e9 igual a 0,5 segundo<\/b><\/span><\/span><\/span>, ent\u00e3o o modulo da <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o centr\u00edpeta<\/b><\/span><\/span><\/span><\/p>\n

de um ponto da <\/b><\/span><\/span><\/span>periferia da rodada bicicleta \u00e9 inferior a 50 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

02-(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Na <\/b><\/span><\/span><\/span>situa\u00e7\u00e3o apresentada<\/b><\/span><\/span><\/span>, o <\/b><\/span><\/span><\/span>per\u00edodo<\/b><\/span><\/span><\/span> do movimento da <\/b><\/span><\/span><\/span>roda da bicicleta \u00e9 superior a 0,5 segundo.<\/b><\/span><\/span><\/span><\/p>\n

03-(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Na <\/b><\/span><\/span><\/span>situa\u00e7\u00e3o apresentada,<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>gr\u00e1fico abaixo<\/b><\/span><\/span><\/span>ilustra a <\/b><\/span><\/span><\/span>velocidade escalar de um ciclista<\/b><\/span><\/span><\/span>, em fun\u00e7\u00e3o do <\/b><\/span><\/span><\/span>tempo<\/b><\/span><\/span><\/span>, ao pedalar uma<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

bicicleta. <\/b><\/span><\/span><\/span>As <\/b><\/span><\/span><\/span>massas da bicicleta e do ciclista <\/b><\/span><\/span><\/span>s\u00e3o, respectivamente, iguais a <\/b><\/span><\/span><\/span>10 kg e a 70 kg.<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>partir dessas informa\u00e7\u00f5es<\/b><\/span><\/span><\/span>, e considerando que a <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o gravitacional local seja de 10 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>, julgue <\/b><\/span><\/span><\/span>os itens de <\/b><\/span><\/span><\/span>04 a 06, fa\u00e7a <\/b><\/span><\/span><\/span>o que se pede no item <\/b><\/span><\/span><\/span>07, <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>assinale a op\u00e7\u00e3o correta <\/b><\/span><\/span><\/span>no item <\/b><\/span><\/span><\/span>08.<\/b><\/span><\/span><\/span><\/p>\n

04-(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Considere que <\/b><\/span><\/span><\/span>uma pessoa <\/b><\/span><\/span><\/span>pule verticalmente na <\/b><\/span><\/span><\/span>garupa <\/b><\/span><\/span><\/span>deuma bicicleta que se desloca com <\/b><\/span><\/span><\/span>velocidade constante v.<\/b><\/span><\/span><\/span><\/p>\n

Nesse caso, <\/b><\/span><\/span><\/span>se a massa dessa pessoa e igual \u00e0 soma das massas do ciclista e da bicicleta<\/b><\/span><\/span><\/span>, ent\u00e3o a <\/b><\/span><\/span><\/span>velocidade final da bicicleta \u00e9 igual a v\/2.<\/b><\/span><\/span><\/span><\/p>\n

05-(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

No <\/b><\/span><\/span><\/span>intervalo de 0 s a 20 s,<\/b><\/span><\/span><\/span> o ciclista <\/b><\/span><\/span><\/span>percorre mais de 84 m.<\/b><\/span><\/span><\/span><\/p>\n

06-(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Considere que o <\/b><\/span><\/span><\/span>selim esteja fixado \u00e0 bicicleta por meio de uma mola ideal<\/b><\/span><\/span><\/span>, de <\/b><\/span><\/span><\/span>constante el\u00e1stica igual a 56.10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span> N\/m.<\/b><\/span><\/span><\/span><\/p>\n

Nesse caso, se a bicicleta passa por um <\/b><\/span><\/span><\/span>buraco <\/b><\/span><\/span><\/span>e, com o <\/b><\/span><\/span><\/span>solavanco, a mola encolhe 5 cm<\/b><\/span><\/span><\/span>, ent\u00e3o a <\/b><\/span><\/span><\/span>profundidade do buraco \u00e9 menor que 11 cm.<\/b><\/span><\/span><\/span><\/p>\n

07-(UnB-DF-015)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Calcule o <\/b><\/span><\/span><\/span>trabalho <\/b><\/span><\/span><\/span>realizado pelo sistema <\/b><\/span><\/span><\/span>ciclista-bicicleta nos primeiros 4 segundos<\/b><\/span><\/span><\/span> de deslocamento. <\/b><\/span><\/span><\/span>Multiplique<\/b><\/span><\/span><\/span> o resultado obtido por <\/b><\/span><\/span><\/span>0,1.<\/b><\/span><\/span><\/span> Depois de efetuados todos os c\u00e1lculos<\/b><\/span><\/span><\/span><\/p>\n

solicitados, <\/b><\/span><\/span><\/span>despreze<\/b><\/span><\/span><\/span>, para marca\u00e7\u00e3o no Caderno de Respostas, a <\/b><\/span><\/span><\/span>parte fracionaria<\/b><\/span><\/span><\/span> do resultado final obtido, caso exista. <\/b><\/span><\/span><\/span><\/p>\n

08-(UnB-DF-015)<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

Com base nos <\/b><\/span><\/span><\/span>dados fornecidos<\/b><\/span><\/span><\/span>, assinale a <\/b><\/span><\/span><\/span>op\u00e7\u00e3o correspondente ao gr\u00e1fico <\/b><\/span><\/span><\/span>que representa o comportamento da <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o da bicicleta no intervalo de 0 s a 20 s.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

(UnB-DF-015)<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

Considerando a <\/b><\/span><\/span><\/span>figura abaixo<\/b><\/span><\/span><\/span>, que ilustra uma bicicleta fazendo uma curva, com <\/b><\/span><\/span><\/span>velocidade<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

constante, em um plano inclinado, com atrito<\/b><\/span><\/span><\/span>, fa\u00e7a o que se pede no item a seguir.<\/b><\/span><\/span><\/span><\/p>\n

09-(UnB-DF-015)<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

No diagrama esquematizado abaixo, <\/b><\/span><\/span><\/span>CM \u00e9 o centro de massa do conjunto ciclista-bicicleta.<\/b><\/span><\/span><\/span> Nesse diagrama, <\/b><\/span><\/span><\/span>desenhe as for\u00e7as que mantem a bicicleta realizando a curva<\/b><\/span><\/span><\/span>. Em seu desenho, <\/b><\/span><\/span><\/span>identifique as for\u00e7as pelos respectivos nomes.<\/b><\/span><\/span><\/span><\/p>\n

(UnB-DF-015)<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

A figura abaixo ilustra a situa\u00e7\u00e3o em que um ciclista realiza <\/b><\/span><\/span><\/span>um salto<\/b><\/span><\/span><\/span> cuja trajet\u00f3ria descreve uma <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

par\u00e1bola. <\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>bicicleta <\/b><\/span><\/span><\/span>utilizada pelo ciclista tem uma <\/b><\/span><\/span><\/span>coroa dentada dianteira<\/b><\/span><\/span><\/span>, movimentada pelos pedais e ligada, pela corrente, a <\/b><\/span><\/span><\/span>coroa dentada de raio menor, chamada catraca<\/b><\/span><\/span><\/span> e <\/b><\/span><\/span><\/span>fixada no eixo da roda<\/b><\/span><\/span><\/span> <\/b>traseira.<\/b><\/span><\/span><\/span> O <\/b><\/span><\/span><\/span>numero de voltas<\/b><\/span><\/span><\/span> realizadas <\/b><\/span><\/span><\/span>pela roda traseira a cada pedalada<\/b><\/span><\/span><\/span> \u00e9 determinado pelo <\/b><\/span><\/span><\/span>tamanho relativo das coroas dentadas.<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>coroa dianteira<\/b><\/span><\/span><\/span> de uma bicicleta de <\/b><\/span><\/span><\/span>6 marchas pode ter 44 dentes<\/b><\/span><\/span><\/span>, e as <\/b><\/span><\/span><\/span>catracas, 12, 14, 16, 18, 21,<\/b><\/span><\/span><\/span> <\/b>26 e 32 dentes.<\/b><\/span><\/span><\/span> O <\/b><\/span><\/span><\/span>sistema ciclista-bicicleta tem massa de 80 kg<\/b><\/span><\/span><\/span>. A <\/b><\/span><\/span><\/span>velocidade inicial<\/b><\/span><\/span><\/span> do sistema ao <\/b><\/span><\/span><\/span>iniciar o salto \u00e9 de 43,2 km\/h e faz um angulo de 30<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span> com a dire\u00e7\u00e3o horizontal.<\/b><\/span><\/span><\/span><\/p>\n

Internet: <www.mundofisico.joinville.udesc.br> (com adapta\u00e7\u00f5es).<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>partir do texto e da figura acima<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>julgue<\/b><\/span><\/span><\/span> os itens de <\/b><\/span><\/span><\/span>10 a 12.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Considere que a <\/b><\/span><\/span><\/span>acelera\u00e7\u00e3o da gravidade \u00e9 de 10 m\/s<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span> e desconsidere a resist\u00eancia do ar.<\/b><\/span><\/span><\/span><\/p>\n

10-(UnB-DF-015)<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

No <\/b><\/span><\/span><\/span>ponto mais alto da trajet\u00f3ria<\/b><\/span><\/span><\/span>, a <\/b><\/span><\/span><\/span>energia potencial do sistema ciclista-bicicleta \u00e9 inferior a 1.500 J.<\/b><\/span><\/span><\/span><\/p>\n

11-(UnB-DF-015)<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

Se um <\/b><\/span><\/span><\/span>ciclista<\/b><\/span><\/span><\/span>, ao pedalar a bicicleta, <\/b><\/span><\/span><\/span>n\u00e3o estiver usando a catraca de maior numero de dentes<\/b><\/span><\/span><\/span> e quiser <\/b><\/span><\/span><\/span>aumentar a velocidade da bicicleta, sem alterar o ritmo das pedaladas<\/b><\/span><\/span><\/span>, ele deve <\/b><\/span><\/span><\/span>muda<\/b><\/span><\/span><\/span>r para uma catraca que <\/b><\/span><\/span><\/span>tenha que os da catraca em mais dentes uso.<\/b><\/span><\/span><\/span><\/p>\n

12-(UnB-DF-015)<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

Mantendo-se <\/b><\/span><\/span><\/span>constante a velocidade inicial<\/b><\/span><\/span><\/span> do salto, quanto <\/b><\/span><\/span><\/span>maior for o \u00e2ngulo que o sistema<\/b><\/span><\/span><\/span> <\/b>ciclista-bicicleta fizer com a dire\u00e7\u00e3o horizontal, maior ser\u00e1 o alcance do salto.<\/b><\/span><\/span><\/span><\/p>\n

 <\/p>\n

Confira a resolu\u00e7\u00e3o comentada<\/a><\/span><\/h3>\n","protected":false},"excerpt":{"rendered":"

UnB-015 A\u00a0Universidade de Bras\u00edlia (UnB)\u00a0\u00e9 uma\u00a0universidade\u00a0p\u00fablica\u00a0brasileira, com sede na cidade de\u00a0Bras\u00edlia, no\u00a0Distrito Federal\u00a0e com Campus nas cidades de Bras\u00edlia, Planaltina,\u00a0Gama,\u00a0Ceil\u00e2ndia\u00a0e\u00a0Parano\u00e1\u00a0(em projeto). \u00c9 a maior institui\u00e7\u00e3o de ensino superior do\u00a0centro-oeste\u00a0do\u00a0Brasil\u00a0e uma das mais importantes do pa\u00eds. Foi avaliada pelo\u00a0MEC\u00a0atrav\u00e9s do\u00a0\u00cdndice Geral de Cursos\u00a0como a melhor universidade da regi\u00e3o Centro-Oeste, seguida pela\u00a0UFG\u00a0e\u00a0UFGD. (UnB-DF-015) A figura abaixo ilustra, de forma esquematizada, um sistema<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":5,"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-299","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/299","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=299"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/299\/revisions"}],"predecessor-version":[{"id":303,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/299\/revisions\/303"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/5"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=299"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}