Rotational Kinematics-Vinyl Record

[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

Thanks in advance.

 

[dacruick]

Do you know what you are calculating?

 

[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.

 

[dacruick]

No problem, I will help you:).

What units do you expect your answer to be in?

 

[aokidopi]

It is asking in centimeters.

 

[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?

 

[aokidopi]

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

 

[aokidopi]

*0.025

 

[aokidopi]

Thank you dacruick for clearing that up. Doh!

 

[dacruick]

Haha you're welcome