# Rotational Motion: Average angular acceleration of a CD

In summary, the average angular acceleration of a maximum-duration CD during its 74.0-min playing time is -0.006 rad/s^2, calculated by subtracting the initial angular velocity from the final and dividing by the time interval. The correct answer has three significant figures.

## 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.

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

gneill said:
Your given values have 3 significant figures. What you've submitted only has one.
Welp that fixed it. Thank you!

gneill

## 1. What is rotational motion?

Rotational motion is the movement of an object around an axis or center point. It is a type of motion that involves circular or curved paths rather than straight lines.

## 2. How is rotational motion measured?

Rotational motion is measured using the concept of angular displacement, which is the change in the angle or position of an object as it rotates around an axis. This can be measured in degrees, radians, or revolutions.

## 3. What is the average angular acceleration of a CD?

The average angular acceleration of a CD can be calculated by dividing the change in angular velocity by the time it takes for that change to occur. It is typically measured in units of radians per second squared (rad/s^2).

## 4. How does a CD rotate?

A CD rotates around its center point, which is also known as its axis of rotation. This rotation is caused by the friction between the CD and the surface it is placed on, as well as any external forces acting on it.

## 5. What factors affect the average angular acceleration of a CD?

The average angular acceleration of a CD can be affected by various factors, such as the surface it is placed on, the amount of friction present, and any external forces acting on it. Additionally, the shape and size of the CD can also impact its rotational motion.

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