Hey again. It's that time of week, and once again I'm stumped. There are three problems, but we'll take them one at a time. The first is as follows: A certain CD has a playing time of 68 minutes. When the music starts, the CD is rotating at an angular speed of 4.8x10^2 revolutions per minute (rpm). At the end of the music, the CD is rotating at 2.1x10^2 rpm. Find the magnitude of the average angular acceleration of the CD. Express your answer in rad/s^2. What I've tried is to take the difference of the angular displacement (each divided by 60 to change to seconds), multiplied this by 2pi to change to radians, and divide that difference by 68 minutes (4080 seconds). The answer I get is -0.0069 rad/s^2...but this is wrong :uhh: Here's the 'layout': ((210rpm-480rpm)/60s)*2pi)/(4080s)=-0.0069 What have I done wrong?? Thanks in advance.