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Homework Help: Finding revolutions per minute

  1. Sep 16, 2009 #1
    1. The problem statement, all variables and given/known data

    An astronaut is rotated in a centrifuge of radius 4.0 m.

    2. Relevant equations

    v = omega * radius

    a = v^2/radius

    3. The attempt at a solution

    Ok, so I first found the omega for this acceleration, which came out to be

    omega = 3.56179 s^-1

    then I decided that since the it is revolutions per minute, I multiplied the vaule of omega by 60 seconds, and divided the value by the circumference of the circle.

    (2*pi*4)/210.107 = .119619

    So this answer is completely wrong because it does not make any sense whatsoever
  2. jcsd
  3. Sep 16, 2009 #2
    You need to know more data to work out the rpm, knowing just the radius of the centrifuge is not enough.
  4. Sep 16, 2009 #3
    This was all that was given to me.
  5. Sep 16, 2009 #4
    Omega = 2pi / Time, then you can get the time of one revolution
  6. Sep 16, 2009 #5
    Well rpm for a gven radius can infinetly many values. How did you work out the value of omega?
  7. Sep 16, 2009 #6
    I used a = V^2/r since i have acceleration and r

    Once I got the value of V, i substitute it into v = omega * radius and solved for omega.
  8. Sep 16, 2009 #7
    You have forgotten to state the value of a in the question above.
  9. Sep 16, 2009 #8
    Oh ok, well then just use your value of omega in the formula anden gave you. That is the time for 1 revolution.
  10. Sep 16, 2009 #9
    Sorry, the acceleration is 5g
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