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Tensions with 3 blocks on a single pulley

  1. Sep 22, 2015 #1
    1. The problem statement, all variables and given/known data

    The diagram shows two blocks, each of mass m, connected by cord A, and the top block of mass m connected to the block of mass M by cord B. Both cords are of negligible mass. Cord B passes over a frictionless peg that is fixed in place. The system of blocks and cords is released from rest from the position shown, and because 2m<M, block M descends under constant acceleration the distance h in a time T. Derive, in terms of m, M, h, T, and the acceleration due of gravity g, expressions for the tensions in the cords A and B during that time T
    pulley.png



    upload_2015-9-22_21-30-25.png


    2. Relevant equations


    3. The attempt at a solution
    The picture shows my work. And I was wondering if I drew the FBD correctly and my equations were correct
     
  2. jcsd
  3. Sep 23, 2015 #2

    Doc Al

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    Staff: Mentor

    (1) In your FBD for mass 2, you left out the tension from the cord below it.
    (2) When writing your equations, take care to use a consistent sign convention for the acceleration.
     
  4. Sep 23, 2015 #3
    So tension A= m(a+g)
    And
    Tension B= M(g-a)
     
  5. Sep 23, 2015 #4

    Doc Al

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    Staff: Mentor

    Those are correct.
     
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