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Homework Help: Two masses connected via pulley: find acceleration

  1. Feb 16, 2007 #1
    1. The problem statement, all variables and given/known data
    Two masses A and B, and of mass 1.6kg and 2.4kg respectively are connected by a light string which passes over a frictionless pulley. Calculate the acceleration of the 1.6kg mass.


    2. Relevant equations



    3. The attempt at a solution
    To get started I must know whether the two masses both have the same acceleration. Is that true? I know the tension of the system is the same.

    Assuming it's true I get a simultaneous equation that looks like
    16-T=1.6a
    24-T=2.4a

    which works out for a=10m/s^2 and T=0 which is a bit fishy. But if a is different for each mass than there are 3 variables but only two equations.
     
  2. jcsd
  3. Feb 16, 2007 #2

    cristo

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    The two masses have the same acceleration (they are connected by a string!) The smallest mass will move upwards, so its resultant force will be T-16, hence your first equation should read T-16=1.6a
     
  4. Feb 16, 2007 #3
    I see. The system should have a predetermined positive, negative direction. It's not the case that upwards is always + and downwards always - in this pulley problem.
     
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