What is the drill's angular acceleration?

[algorith01]

Homework Statement

A high-speed drill rotating ccw at 2200rpm comes to a halt in 2.80 s. What is the drill's angular acceleration?

Homework Equations

(where w = angular velocity)
w = 2╥/T
v = wr
a = v^2/r
a = w^2*r

The Attempt at a Solution

I start by calculating w. So first I took it to rev per second and then second per revolution which came to be 0.027 seconds per revolution. So w = 2╥/0.027 = 232.71 radians. Now I'm stuck because I don't have r (radius). I've tried going backwards to get r from v, but to no success since v depends in r as r depends in v. Every equation relating to acceleration seems to need r but I don't see how I can get it. Any ideas would be appreciated. Thanks.

 

[rock.freak667]

you don't need radius or linear velocity.

$$\alpha = \frac{\omega_f - \omega_i}{t}$$

 

[algorith01]

Thank you. I realized after you posted that equation that it was a nonuniform circular motion problem, I was going about it the wrong way.