The kinetic energy of a body is given by

Answer

B

Explanation

Initial angular velocity=20 rd/s Therefore `alpha=2rad/s^2`
`rarr t_1=omega/alpha_1=20/2=10sec`
Therefore 10 sec it wil come to rest.
Since the same torque is continues to act on the body it will produce same angular acceleration and since the initial kinetic energy= the kinetic energy at a instant.
So initial angular velocity.
=angular velocity at that instantgt
Therefore time require to come to that angular velocity
`t_2=omega_2/alpha_2=20/2=10sec`
therefore, time required
`=t_1+t_2=20sec`