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Homework Help: Rotational Kinematics-Vinyl Record

  1. Nov 1, 2011 #1
    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.
  2. jcsd
  3. Nov 1, 2011 #2
    Do you know what you are calculating?
  4. Nov 1, 2011 #3
    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.
  5. Nov 1, 2011 #4
    No problem, I will help you:).

    What units do you expect your answer to be in?
  6. Nov 1, 2011 #5
    It is asking in centimeters.
  7. Nov 1, 2011 #6
    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?
  8. Nov 1, 2011 #7
    Oh...800 revolutions is 20 cm. So 0.25 cm per groove?
  9. Nov 1, 2011 #8
  10. Nov 1, 2011 #9
    Thank you dacruick for clearing that up. Doh!
  11. Nov 1, 2011 #10
    Haha you're welcome :smile:
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