(a) 4.03 s
The initial angular velocity of the wheel is

The angular acceleration of the wheel is

negative since it is a deceleration.
The angular acceleration can be also written as

where
is the final angular velocity (the wheel comes to a stop)
t is the time it takes for the wheel to stop
Solving for t, we find

(b) 27.6 rad
The angular displacement of the wheel in angular accelerated motion is given by

where we have
is the initial angular velocity
is the angular acceleration
t = 4.03 s is the total time of the motion
Substituting numbers, we find
