(PUC-PR) O físico e engenheiro francês Nicolas Léonard Sadi Carnot (1796-1832), em seu trabalho Reflexões sobre a potência motriz do fogo, concluiu que as máquinas térmicas ideais podem atingir um rendimento máximo por meio de uma sequência específica de transformações gasosas que resultam num ciclo – denominado de ciclo de Carnot, conforme ilustra a figura a seguir.

A partir das informações do ciclo de Carnot sobre uma massa de gás, conforme mostrado no gráfico p x V analise as alternativas a seguir.

I. Ao iniciar o ciclo (expansão isotérmica 1 → 2) a variação de energia interna do gás é igual a Q_q e o trabalho é positivo.

II. Na segunda etapa do ciclo (expansão adiabática 2 → 3) não há troca de calor, embora o gás sofra um resfriamento, pois ∆U = W.

III. Na compressão adiabática 4 → 1 última etapa do ciclo, o trabalho realizado sobre o gás corresponde à variação de energia interna dessa etapa e há um aquecimento, ou seja, ∆U=+W

IV. O trabalho útil realizado pela máquina térmica no ciclo de Carnot é igual à área A ou, de outro modo, dado por: W = Q_Q - Q_F

V. O rendimento da máquina térmica ideal pode atingir até 100% pois o calor Q_F pode ser nulo – o que não contraria a segunda lei da termodinâmica.

Estão CORRETAS apenas as alternativas:

Read this text about Yuri Gagarin.

Yuri was born on March 9, 1934 in Klushino, a small village 100 miles west of Moscow. His father was a cabinetmaker, carpenter, bricklayer, and farmer, and his mother was a milkmaid. Together they worked on a kolkhoz or collective farm. By Soviet social standards, his heritage was impeccable. He was the third of four children. During the war, the Nazis threw his family out of their home and took away two of his sisters. Yuri helped his parents dig a dugout where they lived untill the war was over, then the family moved to Gziatsk. 

[…] 

Yuri was subjected to extremely rigorous training: physical, mental, and psychological. He underwent long periods in a sensory deprivation chamber, experiments with weightlessness, endurance in heat chambers, and test flights under stress with every reaction monitored. […] 

"During the days of preparation for the launch, when everyone had more than his share of concerns, apprehensions, and anxieties, he alone seemed to keep calm. More than that: he was full of good spirits and beamed like the sun." 

On April 12, 1961 the first earthling escaped the gravity well of planet earth. In the spaceship Vostok 1, Senior Lieutenant Yuri Alexeyevich Gagarin orbited earth one time at an altitude of 187 3/4 miles (302 kilometers) for 108 minutes at 18,000 miles an hour. He was the first man to see that the earth was indeed round, indeed mostly water, and indeed magnificent. 

Following his return to earth, Yuri's triumphant walk through Red Square in front of a crowd of hundreds of thousands made him more nervous and afraid than his historic flight. As he reached the podium, the awaiting Valya tearfully whispered in his ear, "Our dream has come true, Yuri." Embracing her he replied, "You're a smart girl! Thank you!" [...]

Russian Archives Online

Disponível em: <http://www.russianarchives.com/gallery/gagarin/>. Acesso em: 19 mar. 2014. (Fragmento)

Rewrite some clauses from the text in just one sentence and set the chronological order for the events according to the text. The beginning of each sentence was given.

A) Yuri helped his parents dig a dugout where they lived / the war was over.

Before the war was over, __________________________________________________________

______________________________________________________________________________

B) Yuri was subjected to extremely rigorous training / He underwent long periods in a sensory deprivation chamber. 

After Yuri had been subjected to extremely rigorous training ______________________________

______________________________________________________________________________

C) Senior Lieutenant Yuri Alexeyevich Gagarin orbited earth one time at an altitude of 187 3/4 miles (302 kilometers) for 108 minutes at 18,000 miles an hour / the first earthling escaped the gravity well of planet earth 

When Senior Lieutenant Yuri Alexeyevich Gagarin orbited earth ___________________________

______________________________________________________________________________

______________________________________________________________________________

D) He reached the podium / the awaiting Valya tearfully whispered in his ear: "Our dream has come true, Yuri." 

After he had reached the podium, ___________________________________________________

______________________________________________________________________________

______________________________________________________________________________

(UFPR) João viaja semanalmente de ônibus e a esposa costuma ir de automóvel a seu encontro na estação rodoviária de Matinhos, onde ele chega pontualmente, e ambos se encontram exatamente às 18h. Um dia, João chega às 17h30min e resolve andar em direção a sua casa pelo caminho que costuma seguir com a sua mulher, mas sem avisá-la. Encontram-se no caminho, ele sobe no carro e os dois voltam para casa, chegando 10min antes do horário de costume. Supondo que sua esposa viajou com velocidade constante e que saiu de casa no tempo exato para encontrar o marido às 18h na estação rodoviária, assinale a alternativa que apresenta o tempo, em minutos, que João andou antes de encontrar-se com ela.

Um prisma regular hexagonal homogêneo com peso de 15 N e aresta da base de 2,0 m e mantido de pé graças ao apoio de um dos seus vértices da base inferior (ver figura) e a ação de uma força vertical de suspensão de 10 N (não mostrada).

Nessas condições, o ponto de aplicação da força na base superior do prisma encontra-se: