# Rotational Motion: Average angular acceleration of a CD

## Homework Statement

"A compact disc (CD) stores music in a coded pattern of tiny pits 10−7m 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."

rinside=.025m
routside=.058m
v=1.25m/s
Calculated from previous parts of this problem:
t=74min=74*60s

α=(ωfi)/(Δt)

## The Attempt at a Solution

I figured average angular acceleration would be calculated by subtracting the initial angular velocity from the final and dividing by the time interval, so I plugged in and performed this calculation:

to get -0.006 rad/s2. This is online homework and it told me my answer is incorrect. I can't tell what I'm doing wrong. I've tried submitting both -0.006 and 0.006.

gneill
Mentor
Your given values have 3 significant figures. What you've submitted only has one.