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Pulling mass with motor through pulley (with mass)

  1. Oct 13, 2013 #1
    1. The problem statement, all variables and given/known data

    http://puu.sh/4PDPV.png [Broken]

    2. Relevant equations

    τ = I*α
    τ = r*F

    3. The attempt at a solution

    EDIT2: Nevermind, manipulated the torque equations wrong, got it now

    EDIT: Tried again and ended up with an actual answer, but still got it wrong :/
    This is the FBD I used http://puu.sh/4PH7l.png [Broken]

    m = 1060 kg
    Ft2 = 10900
    I = 75.5 kg*m^2
    r = 0.757 m


    1060a = Ft1 - 1060*9.81

    τ = I*r*a
    τ = r*F
    F = 10900 - Ft1

    I*r*a = r*F
    I*a = F

    75.5*a = 10900 - Ft1

    1060a = Ft1 - 1060*9.81
    Ft1 = 1060a + 1060*9.81

    75.5a = 10900 - Ft1
    75.5a = 10900 - (1060a + 1060*9.81)
    75.5a = 10900 - 1060a - 1060*9.81
    1060a + 75.5a = 10900 - 1060*9.81
    a = (10900 - 1060*9.81) / (1060 + 75.5)
    = 0.44157
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 13, 2013 #2

    Simon Bridge

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    You need two free-body diagrams.
    You are given the forces on the pulley and the mass
    - just sketch out the fdb's and look at what forces are present.
     
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