# Average angular acceleration of a CD

1. Mar 3, 2007

### cycam

1. The problem statement, all variables and given/known data
Compact Disc. A compact disc (CD) stores music in a coded pattern of tiny pits 10^-7 m deep. The pits are arranged in a track that spirals outward toward the rim of the disc; the inner and outer radii of this spiral are 25.0 mm and 58.0 mm, respectively. As the disc spins inside a CD player, the track is scanned at a constant linear speed of 1.25 m/s.

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
alpha = (w_out - w_in)/ t

3. The attempt at a solution

I found the angular speeds of the inner and outer radii, but I'm not sure how to apply it to this problem. When I plug in the values into the equation above, I get -0.006 rad/s^2 from [(21.55-50)rad/s]/ [(74min)(60s/min)], which seems to be the incorrect answer.

Any help would be appreciated :] Thanks in advance.

Last edited: Mar 3, 2007