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Homework Help: Angular Velocity of Discus

  1. Oct 1, 2008 #1
    1. The problem statement, all variables and given/known data
    To throw the discus, the thrower holds the discus with a fully outstretched arm and makes one revolution as rapidly as possible to give maximum speed to the discus at release. The diameter of the circle in which the discus moves is about 1.7m.

    If the thrower takes 1.0s to complete one revolution, starting from rest, what will be the speed of the discus at release?

    2. Relevant equations

    3. The attempt at a solution I found the angular acceleration to be 2pi rad/s. I just dont know how to find the speed from there..
  2. jcsd
  3. Oct 1, 2008 #2


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    Homework Helper

    Hi rebeccc,

    I don't believe that angular acceleration is correct. What equations and numbers did you use to find it?
  4. Oct 2, 2008 #3
    Okay, I re-worked it and found the angular acceleration to be 6.28 rad/s^2. I just don't know where to go from here to find the speed of the discus when it is released...
  5. Oct 2, 2008 #4
    If anyone has any ideas.. I need help asap!
  6. Oct 2, 2008 #5
    assuming your angular acceleration is correct. You can use the formula

    [tex] \omega_f = \omega_i + \alpha t [/tex]
  7. Oct 2, 2008 #6
    I have to have my answer in m/s which is really throwing me off.. I don't know how to get to m/s from rad/s. = (
  8. Oct 2, 2008 #7
    Ahh so it wants the tangential velocity.
    well think about what omega is.
    It's radians per second. Then think about exactly what a radian is.

    1 radian is the arc length of the radius, so the total length of 1 radian = that of the radius.

    Hint #2:
    therefore omega = v/r
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