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Homework Help: A spool of thin wire pivots on a shaft

  1. Oct 23, 2012 #1
    1. The problem statement, all variables and given/known data
    Pulley with Friction
    A spool of thin wire pivots on a shaft, and there is friction. The wire is pulled by a hanging mass M of 1.30 kg. After falling a distance D= 1.7 m starting from rest, the mass has a speed of 0.065 m/s. Calculate the energy lost to friction during that time.
    Inner radius, ri = 0.50 m
    Outer radius, r0 = 0.65 m
    Icm= 0.96 kg/m2.

    3. The attempt at a solution

    a=v^2/2*D -> a=0.0036
    T=m(g-v^2/2*D) -> T=12.24
    alpha=a/r0=(r0*T-Qf)/Icm -> Qf=7.951
    theta=D/r0 ->2.62
    Ef=theta*Qf -> Ef=20.83

    what am I doing wrong?
  2. jcsd
  3. Oct 24, 2012 #2


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    Science Advisor
    Homework Helper

    Hi SereneKi! :smile:

    I don't understand the question …

    is there a pulley and a spool?

    between what surfaces is the friction?

    what is the relevance of the outer radius of the spool? :confused:
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