Angular Velocity Problem

[quicknote]

I'm having problems with parts b and c...

At time t= 0 a grinding wheel has an angular velocity of 22.0 rad/s . It has a constant angular acceleration of 26.0 rad/s^2 until a circuit breaker trips at time t= 2.30 s . From then on, the wheel turns through an angle of 436 rad as it coasts to a stop at constant angular deceleration.

a. Through what total angle did the wheel turn between and the time it stopped?
Express your answer in radians.

\Delta \Theta = 13t^2 + 22t at t=2.3s is 119.4rad
Therefore total angle is 119 + 436 = 555rad

b. At what time does the wheel stop?
Express your answer in seconds.

So I know that \omega_{f} = 0 for the wheel to stop
\omega_{i} = 22.0 rad/s
That's as much as I understand...

c. What was the wheel's angular acceleration as it slowed down?
Express your answer in radians per second per second.

Would I use this equation \omega_{f} = \omega_{i} + \alpha t
and just solve for \alpha?
[tex] \omega_{f} = 0
\omega_{i} = 22.0
t = time solved in part b [\tex]

[Päällikkö]

b)
Supposing I understood the problem right (I'm unfamiliar with the term grinding wheel):

The equations for constant acceleration are quite similar to the ones in kinematics.
\omega = \omega _0 + \alpha t
\theta = \theta _0 + \omega _0 t + \frac{1}{2} \alpha t^2
Now with two equations and two unknowns, can you solve for t ?