Frictional Torque Flywheel Question

[Schoomy]

Homework Statement

A spinning flywheel has rotational inertia I = 403.8 kg · m2. Its angular velocity decreases from 20.0 rad/s to zero in 256.8 s due to friction. What is the frictional torque acting?

The Attempt at a Solution

I tried using Vt = r |w| and Wav = change in theta / change in time, to get r, but I'm not sure if that's right,

Then I used I = 1/2mr^2 to get mass.

Finally, I used F=ma to get Force, using the mass found above and acceleration = change in velocity (aka 20*57) / change in time.

Then I had force and radius for plugging into torque = radius*force.

 

[rl.bhat]

Using w = wo + alpha*t, find alpha.
Torque = I*alpha.