Question

A body has a moment of inertia = 5kgm^2 about an axis. What should be the torque for increasing its angular speed from 0 to 10rad/s in 4s? Assume that the body rotates purely about that axis.

(a) 25Nm

(b) 2.5Nm

(c) 12.5Nm

(d) 1.25Nm

The question was posed to me at a job interview.

The origin of the question is Kinematics of Rotational Motion about a Fixed Axis in portion System of Particles and Rotational Motion of Physics – Class 11

Answer 1

The correct choice is (c) 12.5Nm

For explanation: w = w0 + a*dt OR 10 = 0 + a(4)

∴ a = 2.5 rad/s^2.

Torque = Ia = 5*2.5 = 12.5Nm,      

where ‘I’ is the moment of inertia.