What does it mean to say that two systems are in thermal equilibrium?

a. The two objects are at the same temperature

B. The two objects, if they are in thermal contact, would have no heat flow between them.

C. The two objects, not in thermal contact, would not have heat flow even if they were brought into thermal contact with each other.

d. All of the answers

One method of getting a tight fit, say of a metal peg in a hole in a metal block, is to manufacture the peg slightly larger than the hole. The peg is then inserted when at a different temperature than the block. Should the block be hotter or colder than the peg during insertion?

A. Hotter block, colder peg.

B. Colder block, hotter peg.

C. They should be at thermal equilibrium with each other.

D. For this procedure to be effective, they should both be hot.

E. For this procedure to work, they should both be cold.

Find out the human population of Earth. Is there a mole of people inhabiting Earth? If the average mass of a person is 60 kg, calculate the mass of a mole of people. How does the mass of a mole of people compare with the mass of Earth?

a. There is a small fraction of a mole's worth of people on the Earth right now, but if you had a mole's worth of 60 kg people, their mass would be about 6 times that of the entire planet.

B. The Earth's population is several moles worth of people and we account for half of the Earth's present mass.

C. There is a small fraction of a mole's worth of people, but one mole of people would only account for 1/6 of the Earth's mass.

D. The Earth's population is approximately 2.3 moles of people, the mass of these people is about 1/6 of the Earth.