At t = 0 a grinding wheel has an angular velocity of 21.0 rad/s. It has a constant angular acceleration of 21.0 rad/s^2 until a circuit breaker trips...

At t = 0 a grinding wheel has an angular velocity of 21.0 rad/s. It has a constant angular acceleration of 21.0 rad/s^2 until a circuit breaker trips at 2.40 s. From then on it turns through 344 rad as it coasts to a stop at constant acceleration.