Physics 115A Answers to assigned questions from chapter 15, Giancoli
1. Some of the internal energy (equal to the heat of vaporization) is emitted to the
environment. Heat is exchanged, but no work is done.
3. Since Q - W = 0 here, if W = 3700 J, then Q = 3700 J.
5. Yes. This is true of every isothermal process. See Questions 3 and 4 above.
8. No. A household refrigerator pumps thermal energy from its inside into the
room and therefore, the room cannot be cooled that way. However, if the refrigerator
door is left open and you stand in front of it, you will be cooler, while the air behind the
refrigerator will be warmer. On balance, no heat is removed from the room. In fact, it
will be increased by the heat transferred from operation of the compressor motor.
12. In any small local area, to extract energy from the ocean, there would have to be
a heat engine that took ocean water at the ocean temperature and exhausted the water,
also at the (same) ocean temperature. Any such process would violate the Second Law
unless one had access to a lower temperature reservoir than the ocean; and in the local
area, there is no such reservoir.
19. “You can’t get something for nothing” would be a statement of the conservation
of energy: ∆U = Q - W. “You can’t even break even” S = 0 would be breaking even, but
it must be true that S>0 for any real process. Fig. 15-13 shows what breaking even
would imply.