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Homework Help: Yo-Yo Rotation

  1. Apr 27, 2009 #1
    1. The problem statement, all variables and given/known data

    A yo-yo has mass of 400 kg and radius of 1.5m. Its axle of rotation has a radius of 0.1m. Its string is attached to a crane. What is its final velocity after it is released.
    mass (m)=400 kg
    Radius (R)= 1.5 m
    axle of yo-yo (r)= 0.1 m
    height (h)=57m
    angular acceleration (x)= x

    2. Relevant equations

    F=ma; I=(1/2)mr^2; a=xr a/r=x

    3. The attempt at a solution

    F=ma ; Torque=Tr=Ix T=Ix/r

    Fnet,y = mg - T = ma

    mg - I(a/r)/r = ma

    mg = ma + I(a/r)/r

    mg/ (m + I/r^2) = a

    mg/(m + (1/2)mr^2/r^2 ) = a

    a = 6.53 m/s

    This doesnt seem right. Can anyone show me my error?
  2. jcsd
  3. Apr 27, 2009 #2
    well you have calculated the accelertion whereas the question asks for final velocity ...
  4. Apr 28, 2009 #3
    lol . ok figured it out. i was also using lowercase r instead of uppercase R.
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