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Double Atwood Machine (With one end of the string connected to the ground)

  1. Sep 27, 2009 #1
    1. The problem statement, all variables and given/known data[/b
    ]http://teacher.pas.rochester.edu/phy121/PracticeExams/FinalExam/FinalExam_files/image015.jpg
    This is not the exact picture, instead of having M1 there let end of the string be connected to the ground instead
    Find the tensions and accelerations


    2. Relevant equations



    3. The attempt at a solution Hello, i am having a little problem with this question, i attempted to let T3=2(T1), because i thought the normal force tension from the ground and tension from mass 2 would give a tension equal to T1, and then i looked at it again and thought to myself that the acceleration of mass 2 would have to be the same as the acceleration of mass 3 by the conservation of string, because since one end of the second pulley is connected to the ground, the ground will never move up or down so therefore only mass 2 will be able to move and it will have to move the same length as mass 3 and therefore the accelerations will be the same, but that doesnt add up if the tensions are different how can the accelerations be the same, could someone please tell me if i am missing somthing?
     
  2. jcsd
  3. Sep 28, 2009 #2

    tiny-tim

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    Hello mikee! :smile:
    ah, you're saying that the small pulley has only three forces acting on it, which are T3 and T1 twice, and so T3 = 2T1.

    but that only works if the small pulley is not accelerating (and has mass negligible compared with the blocks) :wink:
     
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