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Laws of motion question

  1. Dec 11, 2006 #1
    1. The problem statement, all variables and given/known data
    Having trouble with this problem, cant figure it out!! Please help me!!!
    The persons cast is the green drawing (sorry by i was using ms paint)

    The problem is as follows:
    The leg and cast in the picture above weigh 220N (w1). Determine the weight w2 and the angle a needed so that no force is exerted on the hip joint by the leg plus the cast.

    In case you cant make out the picture, the block on the left is 110N, and the angle is 40DEG on the left. w1 = 220N. the block on the right is w2. with angle a.

    Thank you guys so much!! Im rackin my brain here!

    2. Relevant equations
    Not sure how to even out the two to figure this out, im confused as where to start!

    3. The attempt at a solution
    I dont even know how to begin to setup this problem!!!
  2. jcsd
  3. Dec 11, 2006 #2


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    Not to be gratuitously violent, but conceptually cut off the leg and do the problem with just the leg and the ropes. The rest of the body is not doing anything. Note that the ropes are connected at the center of mass of the leg, which is the only way you can have no force on the hip.
    Last edited: Dec 11, 2006
  4. Dec 11, 2006 #3
    hrm, k, i think i get what your saying... i'll try this out! thanks!
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