Answer
See explanation.
Work Step by Step
By attaching a grinding wheel to the shaft, the shaft’s moment of inertia is increased. That means that when the motor is turned on, and applies a torque to the shaft, the angular acceleration will be smaller than that of the bare shaft.
$$\Sigma \tau = I\alpha$$
$$\alpha = \frac{\Sigma \tau }{I}$$
With a smaller angular acceleration, the shaft takes longer to come up to its final speed.
