### Q.15:- To maintain a rotor at a uniform angular speed of 200 rad s^{–1}, an engine needs to transmit a torque of 180 Nm. What is the power required by the engine?

(Note: uniform angular velocity in the absence of friction implies zero torque. In practice, applied torque is needed to counter frictional torque). Assume that the engine is 100 % efficient.

**Answer:-**Angular speed of the rotor, ω = 200 rad/s

Torque required, τ = 180 Nm

The power of the rotor (*P*) is related to torque and angular speed by the relation:

*P* = τω

= 180 × 200 = 36 × 10^{3}

= 36 kW

Hence, the power required by the engine is 36 kW.