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Homework Help: Pulley, Motor and Weight Torque Problem

  1. Oct 21, 2012 #1
    Pulley and Motor - Torque Problem

    1. The problem statement, all variables and given/known data
    When the motor in the figure below lowers the m = 1140kg mass, it produces a tension of 1.04E+4N in the cable on the right side of the pulley. The pulley has a moment of inertia of 79.7kgm^2 and a radius of 0.741m. The cable rides over the pulley without slipping. Determine the acceleration of the m = 1140kg mass. Use g=9.81m/s^2.
    Draw free-body diagrams of the mass and the pulley. Do not assume that the tension in the cable is the same on both sides of the pulley.

    2. Relevant equations

    a=α*r where α = angular acceleration
    ----> a/r=α

    3. The attempt at a solution
    mg-[itex]T_1{}[/itex] = ma
    [itex]T_2{}[/itex] = 10 400 N

    (11 183 - 11 40a) - (10 400) = (79.7/0.741^2)a
    783-1140a = 145.15a
    783 = 1285.15a
    a= 0.609 m/s/s

    I'm not sure what I'm doing wrong. The steps all make sense to me, but when I've tried submitting the answer on LON-CAPA it says it's incorrect. Anyone have any ideas?
    Last edited: Oct 21, 2012
  2. jcsd
  3. Oct 21, 2012 #2
    Can you add a picture, sketch, or scan of the set-up. One picture is worth a lot of words.
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