Page 162 - Schaum's Outline of Theory and Problems of Applied Physics

CHAP. 12] SIMPLE MACHINES 147

As a general rule, the IMA of a pulley system is equal to the number of strands of rope that support the load. The
rope leaving the upper pulley in Fig. 12-1 does not help to support the load and hence is not counted in determining
the IMA of the system.

SOLVED PROBLEM 12.2
Find the IMA of the pulley system shown in Fig. 12-2.

Fig. 12-2

This pulley system is the same as that in Fig. 12-1 but is inverted. As a result, five strands of rope now support
the load, and the IMA is accordingly 5.

SOLVED PROBLEM 12.3
Find the IMA of the pulley system shown in Fig. 12-3.

Fig. 12-3

There are actually two pulley systems here. The load is initially supported by the two strands of ropes 1 and 2
that pass around pulley A, so IMA 1 = 2. The tension in rope 2 is then supported by strands 3 and 4 of another rope