# Rotational Kinematics-Vinyl Record

1. Nov 1, 2011

### aokidopi

1. In the old days, long before CDs and MP3s, people listened to music using vinyl records. Long-playing vinyl records spin at a constant rate of 33-and-one-third rpm (revolutions per minute). The music is encoded onto a continuous spiral track on the record that starts at a radius of 30 cm from the center and ends at a radius of 10 cm from the center. If a record plays for 24 minutes, how far apart are the grooves in the track on the record?

2. 60 secs=1 min. circumference=2pi(r)

3. The vinyl spins at 33 1/3 revolutions per minute. In 24 minutes, it spins 800 revolutions. A revolution is the 360 degrees of a circle. If the vinyl record travels at a constant rate, the avg. radius it travels at is 20 cm. 20 cm times 2 pi is the avg. circumference. This multiplied by 800 revolutions is approximately 100,000 cm. But this is the incorrect solution

2. Nov 1, 2011

### dacruick

Do you know what you are calculating?

3. Nov 1, 2011

### aokidopi

I thought the grooves were the microscopic indentations of the vinyl. It asks for how far apart the grooves of the track on the record are. I thought this implied the length of the continuous groove. If this is wrong, please help me understand the question.

4. Nov 1, 2011

5. Nov 1, 2011

6. Nov 1, 2011

### dacruick

Yes, I'll help you along. It is asking you how far apart the grooves are in centimetres. So maybe centimetres per groove is an ideal unit for you?

7. Nov 1, 2011

### aokidopi

Oh...800 revolutions is 20 cm. So 0.25 cm per groove?

8. Nov 1, 2011

*0.025

9. Nov 1, 2011

### aokidopi

Thank you dacruick for clearing that up. Doh!

10. Nov 1, 2011

### dacruick

Haha you're welcome