 # A disk rotates about an axis through its center. Point A is located on its rim and point B is located exactly halfway between the center and the rim. What is the ratio of (a) the angular velocity ω A to that of ω B and (b) the tangential velocity v A to that of v B ? ### College Physics

11th Edition
Raymond A. Serway + 1 other
Publisher: Cengage Learning
ISBN: 9781305952300 ### College Physics

11th Edition
Raymond A. Serway + 1 other
Publisher: Cengage Learning
ISBN: 9781305952300

#### Solutions

Chapter
Section
Chapter 7, Problem 1CQ
Textbook Problem

## A disk rotates about an axis through its center. Point A is located on its rim and point B is located exactly halfway between the center and the rim. What is the ratio of (a) the angular velocity ωA to that of ωB and (b) the tangential velocity vA to that of vB?

Expert Solution

(a)

To determine
The ratio of the angular velocity of point A and point B.

The ratio of the angular velocity of point A and point B will be 1 .

### Explanation of Solution

Given Info: The disc is rotating through its center. The point is on the rim of the disc and point B is half way between point A and the center.

Explanation:

When a rigid body is rotating about any axis, all the points in the rigid body have the same angular speed.

Since the dick can be considered to be a rigid body, all the points in it will have equal angular velocity. So the ratio of the angular velocity of point A and point B will be 1 .

Conclusion: The ratio of the angular velocity of point A and point B will be 1 .

Since Andrea and Chunk are in the same circular platform their angular speed cannot be different so option (a) and (c) are not correct.

Expert Solution

(b)

To determine
The ratio of the tangential velocity of point A and point B.

The ratio of the tangential velocity of point A and point B 2 .

### Explanation of Solution

Given Info: The disc is rotating through its center. The point A is on the rim of the disc and point B is half way between point A and the center.

Explanation:

Tangential velocity of a rotating particle is given by,

vt=ωr

• ω is the angular speed

The angular speed of point A and point B is the same. The tangential velocity ratio of point A and point B depends on the ratio of their distance from the center.

vAvB=rArB

• vA is the tangential velocity of point A
• rA is the distance between point A and the center
• vB is the tangential velocity of point B
• rB is the distance between point B and the center

Since the point A is on the rim of the disc and point B is half way between point A and the center,

rArB=2

Hence the ratio of tangential velocities will be,

vAvB=2

Conclusion: The ratio of the tangential velocity of point A and point B 2 .

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