Question

An electric motor exerts a constant torque $5Nm$ on a flywheel by which it is rotated at the rate of $420rpm$. The power of motor is:

• A. $110watt$
• B. $150watt$
• C. $220watt$
• D. $300watt$

Answer 1

Answer: (C)

$220watt$

The electric motor rotates at the rate
$420rpm=420\times \frac{2\pi }{60}rad{s}^{-1}$
Thus we get power of motor:
$P=\tau \times \omega$
$=5\times (420\times \frac{2\pi }{60})=220W$