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Homework Help: Velocity of rotating disc

  1. Mar 1, 2016 #1
    1. The problem statement, all variables and given/known data

    Find the velocity v of a general point on a plate rotating at 800 rpm which is r meters from the center.

    This is literally a copy and paste job.

    2. Relevant equations

    period = T = 1 / f ; f = frequency

    3. The attempt at a solution

    This is what I did please tell me if it is correct

    800 rpm = 40 / 3 rps = f

    T = 1 / f = 3 / 40

    v = distance / time = (2 pi r) / (3 / 40) = (80 pi r) / 3
  2. jcsd
  3. Mar 1, 2016 #2


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    Homework Helper

    That is correct.
    You could also have seen that 40/3 rps can be directly translated into a speed by replacing the r in rps with the distance covered in 1 revolution (2 pi r).
    That would give you the same result ##\frac{80 \pi r}{ 3}##m/sec.
  4. Mar 1, 2016 #3


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    Staff: Mentor

    Yes, that works. You need to carry the "seconds" unit through to the end though. The period T has seconds as its unit.

    Otherwise you'll end up with a "velocity" with units of distance rather than distance/time.
  5. Mar 1, 2016 #4
    Awesome!!! Thank you.
  6. Mar 1, 2016 #5
    Ohh... I see. Thank you
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