Homework set 3

1. The temperature on a cold day is T = -5 C.  What is this temperature in Kelvin?
A: 268      (Correct)
B: 278
C: -278
D: -268

2. When two things having different temperatures are placed in contact, what flows between
them?
A: Work
B: Heat   (Correct)
C: Temperature
D: none of the above

3. After thermal equilibrium between two objects (e.g. hot chili and a can of coke) is reached,
what measurable quantity of the two objects is the same for both?
A: Heat
B: Work
C: Acceleration
D: Temperature    (Correct)

4. According to the "molecular model of matter", as heat energy flows into a substance, the
temperature increases because_______.
A: the potential energy of the molecules increases
B: the individual molecules become larger.
C: the kinetic energy of the molecules increases.      (Correct)
D: none of the above

5. The heat capacity of water is 1 calorie per gram per C.  How many Joules of energy are needed
to raise the temperature of 1 gram of water by 1 C?
A: 0.239
B: 1055
C: 4.18     (Correct)
D: none of the above

6. The heat capacity of a certain metal is c = 0.1 calorie /g-C.  If I drop a certain amount of this
metal into a cup containing an equal mass of very hot water, by how much will the temperature of
the metal change for every degree C of temperature that the water changes?
A: 0.1 C
B: 10 C      (Correct)
C: 1 C
D: none of the above

7. A heat engine burns 1000 Joules of fuel every cycle, and does 200 Joules of work.  How much
waste heat does it produce every cycle?
A: 800     (Correct)
B: 1200
C: 5
D: none of the above

8. What property of matter allows heat to be turned into work?
A: Mass
B: Heat capacity
C: Thermal expansion    (Correct)
D: none of the above.

9. A heat engine burns 3000 Joules of heat energy and does 500 Joules of work every cycle. 
What is the engine's efficiency?
A: 17 %       (Correct)
B: 83 %
C: 60 %
D: none of the above

10. A steam boiler can sustain temperatures up to 1000 K.  If the average temperature outside is
250 K (Siberia, maybe?), what is the absolute best efficiency I could expect from a steam engine
hooked up to this boiler?
A: 75%         (Correct)
B: 25%
C: 50%
D: none of the above