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Homework Help: Can someone check my solution to this block and tackle problem

  1. Sep 27, 2010 #1
    1. The problem statement, all variables and given/known data

    you absolutely need to check the link for my problem picture; this is a snapshot of my online book.

    http://s861.photobucket.com/albums/ab174/alkaline262/?action=view&current=prob9-1.jpg



    2. Relevant equations

    f=ma



    3. The attempt at a solution

    as you can see from the picture I have let each of the strings dangling be represented by an x value

    so:

    3x1 + x2 = length of rope

    differentiating twice

    3a1 + a2 = 0

    and the equations for m1 and m2:

    m1a1 = -3T + m1g

    m2a2 = -T +m2g

    next step is to add these two equations together and set equal to zero

    3(a1 = -3T/m1 + g)

    +(a2 = -T/m2 +g)
    ----------------------

    3a1 + a2 = 4g -T( 9/m1 + 1/m2) = 0

    solving for T = 4g/( 9/m1 + 1/m2)

    then i can just plug this in to the above a1 and a2 equations to get acceleration right??

    and the tension of that tiny little rope below the center pulley till be 2T.

    what do you think? Have I made any mistakes
     
  2. jcsd
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