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Homework Help: Work done by tension on cart

  1. Feb 11, 2009 #1


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    1. The problem statement, all variables and given/known data
    A cart of mass 5 kg is attached to a block of mass 3 kg by a string that passes over a frictionless pulley. The system is initially at rest and we will assume that friction can be ignored. The block falls a distance of 1 m.
    What is the work done on the cart by the string during this fall?

    2. Relevant equations
    W= FD
    W= Change in Kinetic Energy
    K = mgh

    3. The attempt at a solution

    So 3 x 9.81 x 1= 29.43 J
    But this answer is not correct. What am I doing wrong?
  2. jcsd
  3. Feb 11, 2009 #2


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    Science Advisor
    Homework Helper

    HI TG3! :smile:

    You're saying that the work done on the cart is the change in KE of the cart, which is correct.

    But you've used the mass of the block. :redface:
  4. Feb 11, 2009 #3


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    Erm.... as opposed to what? I've tried the mass of the block, the mass of the cart, and the mass of both of them both put together x 9.81, and nothing works...

    Never mind, I figured it out. g x ((m1xm2)/(m1+m2)).
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