Page 98 - Schaum's Outline of Theory and Problems of Applied Physics

CHAP. 7] ENERGY 83

Multiple-Choice Questions

7.1. Power can be expressed in
(a) kg·m/s (c) N·m/s
2
(b) N·m (d) N·m /s 2
7.2. A woman presses against a wall with a force of 10 N for 10 min. The work she does is
(a) 0 (c) 1224 J
(b) 200 J (d) 12 kJ

7.3. To raise a 200-kg steel beam to a height of 10 m on a bridge being built requires work of
(a) 2 kJ (c) 19.6 kJ
(b) 10 kJ (d) 98 kJ

7.4. A total of 15,000 ft·lb of work is used to lift a load of bricks to a height of 50 ft. The weight of the bricks is
(a) 30.6 lb (c) 300 lb
(b) 94.0 lb (d) 2940 lb

7.5. Six kJ of work are used to lift an object to a height of 100 m. The object’s mass is approximately
(a) 600 g (c) 60 kg
(b) 6 kg (d) 600 kg
7.6. A weightlifter raises a 200-kg barbell over his head from the floor, a displacement of 2 m, in 2.2 s. The average power
he develops during the lift is
(a) 0.18 kW (c) 1.78 kW
(b) 0.89 kW (d) 8.62 kW

7.7. A force of 240 N keeps a 900-kg car moving at a constant velocity of 10 m/s. The car’s engine supplies energy to the
car at a rate of
(a) 2.4 kW (c) 45 kW
(b) 12 kW (d) 90.6 kW
7.8. The work a 300-W electric grinder can do in 5.0 min is
(a) 1 kJ (c) 25 kJ
(b) 1.5 kJ (d) 90 kJ

7.9. An 80-lb girl climbs a 12-ft rope in 7.5 s. Her average power output is
(a) 0.13 hp (c) 0.23 hp
(b) 0.19 hp (d) 7.4 hp

7.10. A 150-kg yak has an average power output of 120 W. The yak can go up a mountain 1.2 km high in
(a) 25 min (c) 13.3 h
(b) 4.1 h (d) 14.7 h

7.11. A 700-kg horse is pulling a sled at a velocity of 3.5 m/s. If the horse’s power output is 1.0 hp, the force the horse
exerts on the sled is
(a) 0.16 kN (c) 0.57 kN
(b) 0.21 kN (d) 15.2 kN