Calculating the Average Angular Acceleration of a CD

[SalsaOnMyTaco]

Homework Statement

Unlike the older vinal records which rotated at a constant ω of 33.3 rotations per minute (rpm), compact disks vary their rotation speed during the playing period. A certain CD has a diameter of 12cm and a playing time of 79 minutes. When the music starts, the CD is rotating at 480 rpm. At the end of the music, the CD is rotating at 213 rpm.

What is the magnitude of the average angular acceleration of the disk during this playing period?

Homework Equations

σ=Δω/Δt

The Attempt at a Solution

([213-480/60]*2∏)/79*60= -.00589

Once i typed the answer, it says its wrong

 

[SammyS]

Homework Statement

Unlike the older vinal records which rotated at a constant ω of 33.3 rotations per minute (rpm), compact disks vary their rotation speed during the playing period. A certain CD has a diameter of 12cm and a playing time of 79 minutes. When the music starts, the CD is rotating at 480 rpm. At the end of the music, the CD is rotating at 213 rpm.

What is the magnitude of the average angular acceleration of the disk during this playing period?

Homework Equations

σ=Δω/Δt

The Attempt at a Solution

([213-480/60]*2∏)/79*60= -.00589

Once i typed the answer, it says its wrong

It asks for magnitude ... that's not negative !