# Homework Help: Finding centripetal acceleration of a CD

1. Oct 1, 2012

### bjudia

1. A CD with a diameter of 12.0 cm starts from rest and with a constant angular acceleration of 1.0 rad/sec2 acquires an angular velocity of 5.0 rad/sec. The CD continues rotating at 5.0 rad/sec for 15.0 seconds and then slows to a stop in 12.0 second with a constant angular deceleration. What is the centripetal acceleration of a point 4.0 cm from the center at the time 10.0 seconds from the start?

2. I know constant angular acceleration equations ωf=ωi+αt
Also centripetal acceleration= ω^2r

I really need some help with this, my professor did not explain this at all. I know radius 0.06m. ωi=5.0rad/sec. The answer to the solution is 1.0 m/s^2 but I'm not sure how to get there.

2. Oct 1, 2012

### Nessdude14

You're given the angular velocity (5 rad/sec.) and the radius that the point revolves around (4 cm or .04 m). You just need to plug the values into the centripetal acceleration equation (a=ω2r)

3. Oct 1, 2012

### PhanthomJay

First correct your typo for the radius at the point in question, which is 0.04 m (.06 m is the radius of the disc).

Calculate the angular speed after 10 seconds, then plug it into the appropriate equation for centripetal acceleration. First you must answer: how long does it take reach its speed of 5 rad/sec? You've listed the relevant equations...now please show an attempt.

4. Oct 1, 2012

### bjudia

That makes total sense! I've been blown away for like 2 hours. lol thank you very much

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