# Homework Help: Rotational motion 2

1. Jun 22, 2012

### nbroyle1

In the days before compact discs and MP3 players (ancient history!), music was recorded in scratches in the surface of vinyl-coated disks called records. In a typical record player, the record rotated with a period of 3.6 s. Find the centripetal acceleration of a point on the edge of the record. Assume a radius of 8.89 cm.

Now I need to find the velocity in order to plug it into the equation for centripetal acceleration which is Ac=v^2/r...

How should I go about solving for the velocity so I can get the centripetal acceleration??

2. Jun 22, 2012

### SammyS

Staff Emeritus
What distance does that point on the edge travel in one second?

3. Jun 22, 2012

### nbroyle1

im not sure... So its traveling 2∏ in 3.6s right??

4. Jun 22, 2012

### SammyS

Staff Emeritus
Yes.

Then, how far does the point on the edge travel in 3.6 seconds?

5. Jun 22, 2012

### nbroyle1

360 degrees. So then in one second I think it travels 100 degrees??

6. Jun 22, 2012

### nbroyle1

So I found that the acceleration is 1.745rad/s^2. Then I plugged it into the equation for average acceleration to find the velocity and got 6.28m/s... is this correct??

7. Jun 22, 2012

### SammyS

Staff Emeritus
I don't think so.

What is the circumference of the circle made by the point on the edge?

8. Jun 22, 2012

### nbroyle1

.1778m is the circumfrance

9. Jun 22, 2012

### nbroyle1

how does the circumference help me im confused??