# Homework Help: Compact disk angular acceleration

1. May 6, 2012

### jkhays

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

A compact disc speeds from rest to 5200 rpms in 620 rad. Diameter is 5.0cm
-how many revolutions did it make in this time
-what is the angular acceleration in rad/s^2
-how long does ti take to reach this speed

2. Relevant equations

3. The attempt at a solution
i was able to find the first part by
620(180/π) = 35523 dividing that by 360 and getting 99 revolutions

for the last 2, i am completely lost to where i even begin solving them.

thank you..

2. May 6, 2012

### tiny-tim

welcome to pf!

hi jkhays! welcome to pf!

you can use the usual constant acceleration equations, with angular acceleration velocity and displacement instead of ordinary (linear) acceleration velocity and displacement

3. May 6, 2012

### climb515c

You know ω initial and ω final, and Δθ. You can solve for angular acceleration using one of the kinematics equations for constant acceleration. Once you have alpha you can solve for t.