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Angular velocity, can someone help?

  1. Nov 2, 2012 #1
    1. The problem statement, all variables and given/known data
    a laboratory centrifuge has rotor radius (from center of rotor to sample) of 12.0 cm and typically spins at a rate of 2000 rpm. When switched off, it turns through 50.0 revolutions in coming to rest. Find the value of its average angular acceleration.


    2. Relevant equations



    3. The attempt at a solution
    so far I only turned the rpm to radians/s which is the angular velocity but I wasn't sure what to do next
     
  2. jcsd
  3. Nov 2, 2012 #2

    tiny-tim

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    welcome to pf!

    hi knowledgerich! welcome to pf! :smile:
    you have initial speed, final speed, and total distance, and the question asks for acceleration

    sooo … just use one of the standard constant acceleration equations (but using angle instead of distance) :wink:
     
  4. Nov 2, 2012 #3
    is the radius used in this equation? I came up with (-33^2 rad/s)/(2*100π) = -3.5 rad/s^2
     
  5. Nov 2, 2012 #4

    haruspex

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    No, I think the radius was given you to confuse you. (There ought to be more questions like that IMO.)
    What are the units of the '33'?
     
  6. Nov 3, 2012 #5

    tiny-tim

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    the radius would only be needed if they gave you the tangential (linear) speed instead of the angular speed …

    eg if they said a wire was coming off the wheel at so-many metres per second :wink:
     
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