Page 170 - Schaum's Outline of Theory and Problems of Applied Physics

CHAP. 12] SIMPLE MACHINES 155

Supplementary Problems

12.1. How great a force is needed to lift a 20-kg mass by using the lever shown in Fig. 12-12?

F in
1.2 m

20 kg

5 m

Fig. 12-12

12.2. A bolt is held in the jaws of a pair of pliers. If the bolt is 25 mm from the pivot and a force of 10 N is applied to each
handle 150 mm from the pivot, find the total compressive force on the bolt.

12.3. Find the IMA of the pulley system shown in Fig. 12-13.

12.4. Find the IMA of the pulley system shown in Fig. 12-14.
12.5. Find the IMA of the pulley system shown in Fig. 12-15.

Fig. 12-13 Fig. 12-14 Fig. 12-15

12.6. What is the highest IMA that can be obtained with a system of two pulleys?

12.7. A chain hoist has upper pulleys 4 and 4.5 in. in radius (a) If the hoist is 80 percent efficient, how much force
is needed to raise a load of 200 lb? (b) How much chain must be pulled through the pulleys to raise the load by
2 ft?

12.8. A chain hoist is used to lift a 180-kg engine block by 1.2 m. To do this, a force of 100 N must be applied to the chain
and 30 m of chain pulled through the system. What is the efficiency of the hoist?

12.9. A 200-kg piano on frictionless casters is to be pushed up a 7-m ramp to a loading platform 1 m above the ground.
How much force is needed?