Question

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

• A. 7.46 J
• B. 7400 J
• C. 7.46 erg
• D. 74.6 J

Answer 1

Answer: (D)

Motor makes 600 rotation per minute
$\therefore$ $n=600\frac{rotation}{minute}=10\frac{rev}{\sec }$
$\therefore$ Time required for one rotation $=\frac{1}{10}s$
Energy required for one rotation = power $\times$ time $=\frac{1}{4}\times 746\times \frac{1}{10}$
$=\frac{746}{40}J$
But work done = 40% of input
$=40$%$\times \frac{746}{40}=0.40\times \frac{746}{40}$
$=7.46J$