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Homework Help: Angular velocity-please help

  1. Mar 10, 2010 #1
    1. The problem statement, all variables and given/known data
    a small puck of mass .5kg is executing Uniform constant motion on a friction free horizontal table. The angular frequency of the puck is 10 sec-1 (counter clockwise) and the radius of the circular motion is .8m. the radius stays fixed as the student holds the string in place. he now pulls the string down .5 m and holds it again in place. what work did he do?

    2. Relevant equations

    KE(original)+ W = KE (final)
    inertia of hockey puck on string = mr2
    w = angular velocity
    I = inertia

    3. The attempt at a solution
    KE(original)+ W = KE (final)
    .5(I)w2 +W = KE final
    .5 (.5)(.8)2(102) + W = KE final

    now i have a problem solving for kinetic energy final...
    KE final = .5(.5)(.5)2(102)(w2)
    I cant figure out what w (angular velocity) is...
    please help!!!
  2. jcsd
  3. Mar 10, 2010 #2


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    Homework Helper

    Have you tried using the conservation of angular momentum?
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