Question

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

Options

• 7.46 J

• 74.6 J

• 740 J

• 7400 J

Answer 1

7.46 J

Explanation:

The motor rotates 600 times per minute.

∴ n = 600 `"revolutions"/"minute"` = 10 `"rev"/s`

∴ Time required to complete one revolution = `1/10` s

The amount of energy required for one revolution Equals = power × time

= `1/4 xx 746 xx 1/10 = 746/40` J

But work done = 40% of input

= `40% xx 746/40 = 40/100 xx 746/40` = 7.46 J