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Homework Help: Double atwood

  1. Sep 11, 2012 #1
    1. The problem statement, all variables and given/known data

    I need to find the equation for the accelerations of the masses on a double atwood apartatus.

    2. Relevant equations


    3. The attempt at a solution
    Ok, I made a free body diagram and I think I figure the first part out. The tension on the top rope is twice the lower rope. I get 3 eqations for the forces.
    Note: MassA is on the top pull with B and C on the lower
    2T - MassA * g = MassA * AccelA
    T - MassB * g = MassB * AccelB
    T - MassC * g = MassC * AccelC
    I also get AccelA = -((AccelB+AccelC)/2) because the average of A and B is simply the opposite of A.
    I hope this is all clear and sorry about the formatting. Somehow I'm drawing a blank on solving this system of equations. Im pretty sure I have all that I need but I just can't get it started. Any help is greatly appreciated. Thank you
  2. jcsd
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