Page 171 - Schaum's Outline of Theory and Problems of Applied Physics

156 SIMPLE MACHINES [CHAP. 12

12.10. (a) What kind of simple machine does a screwdriver represent? (b) The handle of a screwdriver is 3 cm in diameter,
and its blade is 6 mm wide. What is its mechanical advantage?

12.11. A screwdriver whose handle is 1 in. in diameter is used to tighten a bolt which has 24 threads per inch. If the
efficiency is 8 percent, find the force exerted on the nut when a force of 3 lb is applied to the handle.
12.12. A 600 rev/min motor is used to operate an air compressor at 200 rev/min through a V-belt drive. If the motor pulley
is 15 cm in diameter, what should the diameter of the compressor pulley be?

12.13. The sprocket wheel on the rear axle of a certain bicycle is 10 cm in diameter, and the sprocket wheel to which the
pedals are attached is 20 cm in diameter. The wheels of the bicycle are 65 cm in diameter. At how many revolutions
per minute must the pedals be turned to travel at 5 m/s?

12.14. A 10-tooth gear drives a 40-tooth gear with an efficiency of 80 percent. (a) When the input gear turns at 8 rpm,
how fast does the output gear turn? (b) When a torque of 30 N · m is applied to the input gear, what is the output
torque?

12.15. A diesel engine that develops 30 kW at 3600 rpm delivers its power through a 4:1 reduction gearbox whose efficiency
is 95 percent. What is the output torque?

Answers to Multiple-Choice Questions

12.1. (b), (c), (d) 12.5. (c)

12.2. (c) 12.6. (a)

12.3. (b) 12.7. (d)
12.4. (b)

Answers to Supplementary Problems

12.1. 47 N 12.9. 280 N

12.2. 120 N 12.10. (a) Wheel and axle (b)5

12.3. 2 12.11. 18 lb
12.4. 2 12.12. 45 cm

12.5. 8 12.13. 73 rev/min

12.6. 3 12.14. (a) 2 rpm (b)96 N·m

12.7. (a) 13.9 lb (b)36 ft 12.15. 0.30 kN·m
12.8. 71%