# Compact Disc Problem

1. Nov 29, 2007

### sukreth

1. The problem statement, all variables and given/known data

The inner and outer radii of a compact disc are 25 mm and 58 mm. As the disc spins inside a CD player, the track is scanned at a constant linear speed of 1.25m/s. The maximum playing time of a CD is 74.0 min. What is the average angular acceleration of a maximum-duration CD during its 74.0-min playing time? Take the direction of rotation of the disc to be positive.

2. Relevant equations

v=wr
angular acceleration=rw^2

3. The attempt at a solution
I tried to integrate wr somehow, but w is not constant.

2. Nov 29, 2007

### G01

You don't need to integrate.

First of all, $$\omega$$, is the angular frequency. Your second formula is wrong. It should read;

$$a=r\omega^2$$ where a is the linear acceleration.

Either way, all you should need to solve this is the first formula.

You know that v=1.25m/s.

Can you use this, and your first formula to find the angular acceleration? If so, it should just be an algebra problem to find the average angular acceleration.