Page 101 - Schaum's Outline of Theory and Problems of Applied Physics

86 ENERGY [CHAP. 7

7.25. An 800-kg car moving at 6 m/s begins to coast down a hill 40 m high with its engine off. The driver applies the brakes
so that the car’s speed at the bottom of the hill is 20 m/s. How much energy was lost to friction?

7.26. One kilogram of water at 0 C contains 335 kJ of energy more than 1 kg of ice at 0 C. What is the mass equivalent of
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this amount of energy?
7.27. Approximately 12 MJ of energy is liberated when 1 kg of dynamite explodes. How much matter is converted to energy
in this process?
7.28. A sedentary person uses energy at an average rate of about 70 W. (a) How many joules of energy does this person
use per day? (b) All this energy originates in the sun. How much matter is converted to energy per day to supply such
a person?

Answers to Multiple-Choice Questions

7.1. (c) 7.11. (b)

7.2. (a) 7.12. (b)
7.3. (c) 7.13. (c)

7.4. (c) 7.14. (d)

7.5. (b) 7.15. (a)
7.6. (c) 7.16. (d)

7.7. (a) 7.17. (b)

7.8. (d) 7.18. (c)

7.9. (c) 7.19. (a)
7.10. (b)

Answers to Supplementary Problems

7.1. No work is done by a net force acting on a moving object when the force is perpendicular to the direction of the
object’s motion.
7.2. Their velocities are the same. The golf ball, which has the greater mass, has the greater KE and PE.

7.3. No work is done because the force on the moon is perpendicular to its direction of motion.

7.4. (a) 21.6 kJ (b) 21.6 kJ

7.5. (a) 800 ft·lb (b) 800 ft·lb (c) 800 ft·lb
7.6. 1.72 kJ