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How to find the the acceleration of the block M?

  1. Feb 8, 2014 #1
    1.The problem statement, all variables and given/known data
    Find the acceleration of the block of mass M in the situation shown.All surfaces are frictionless

    2.The attempt at a solution
    2Mg-2T=2Ma
    T=Mg-Ma
    and T-mgsin30=ma

    But a is cancelled .what to do?
     

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    Last edited: Feb 8, 2014
  2. jcsd
  3. Feb 8, 2014 #2
    T=Mg-Ma

    Mg-Ma-Mgsin30=Ma

    2Ma = 1/2 Mg
    a= 1/4 g

    Not cancelled?
     
  4. Feb 8, 2014 #3
    Sorry, but answer given is g/3.
     
  5. Feb 8, 2014 #4
    Acceleration of which block is denoted by ##a##? Are the accelerations the same for both blocks?
     
  6. Feb 8, 2014 #5
    Oh,sorry.the acceleration of block 2M is a ,so acceleration of M is 2a.
     
  7. Feb 8, 2014 #6
    Do you get the answer with that correction?
     
  8. Feb 8, 2014 #7
    Yes sir,after Bvu's help,it is solved.
     
    Last edited: Feb 8, 2014
  9. Feb 8, 2014 #8

    BvU

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    Don't understand. In the expression T-Mgsin30=Ma a is clearly the acceleration of block M, which is what is asked for. So keep it and change the acceleration of the other block to a/2, like:

    (2M)g - 2T= (2M) (a/2). Bingo!
     
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