Finding the number of revolutions

[aligass2004]

Homework Statement

Starting from rest, a 12cm diameter compact disk takes 2.7s to reach its operating angular velocity of 2005rpm. Assume that the angular acceleration is constant. The disk's moment of inertia is 2.5 x 10-5 kgm^2.
a.) How much torque is applied to the disk?
b.) How many revolutions does it make before reaching full speed?

Homework Equations

t=I(alpha)

The Attempt at a Solution

For part a I used t = I(delta w/delta t). I found w by finding the frequency (33.417rev/s), and then I plugged f into w = (2pi radians)f to get 209.965. I then found torque to be 1.944 x 10-3 Nm. I am unsure of how to solve for part b.

 

[Astronuc]

Refer to this page - http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html

and think about the rotational analogy of starting from rest, achieving a certain velocity at constant acceleration, and the distance traveled.

 

[aligass2004]

I tried using delta theta = wi (delta t) + 1/2(alpha)(delta time)^2. I got 283.453, but that wasn't right.

 

[queenyv2005]

Divide by 2(pi) to put your answer in radians