Sometimes the power is transmitted from one shaft to another, through a number of pulleys, as shown in fig. Consider a pulley 1 driving the pulley 2. Since the pulleys 2 and 3 are keyed to the same shaft, therefore the pulley 1 also drives the pulley 3 which, in turn, drives the pulley 4.

Let

*d*1 = Diameter of the pulley 1,

*N*1 = Speed of the pulley 1 in r.p.m.,

*d*2,* d*3,* d*4, and* N*2,* N*3,* N*4= Corresponding values for pulleys 2, 3 and 4.We know that velocity ratio of pulleys 1 and 2,

Similarly, velocity ratio of pulleys 3 and 4,

Multiplying the above equations gives

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