A quarter horse power motor runs at a speed of 600 r.p.m. Assuming 40% efficiency, then what will be the work done by the motor in one rotation?

Here,

Power is ¼ hp = 746/4 W = 186.5 W

Since, efficiency of motor is 40%,

The power used in doing work is 40% of 186.5 W, so,

P = 186.5 × 40/100

=> P = 74.6 W

Angular velocity of the motor, ω = 600 rpm = 10 rps

=> ω = (600)(2π)/60 rad/s

=> ω = 20π rad/s

Let the torque be τ.

So, P = τω

=> τ = P/ω = 74.6/(20π)

Now,

Work done in 1 rot = (τ)(2π)

=> W = [74.6/(20π)]×(2π)

=> W = 7.46 J