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Homework Help: Two hanging masses supporting object

  1. Nov 30, 2007 #1
    1. The problem statement, all variables and given/known data

    The leg and cast in Figure P4.18 weigh 260 N, with the center of mass as indicated by the blue arrow in the diagram. The counterbalance w2 weighs 115 N. Determine the weight w1 and the angle needed in order that there be no force exerted on the hip joint by the leg plus cast.

    2. Relevant equations

    This is one of the problems; I can't figure out which equations pertain to this problem.

    3. The attempt at a solution

    cot 40 = -x2/115
    x = -137.05

    a^2 + b^2 = c^2
    115^2 + (-137.05)^2 = c^2
    32007.70 = c^2
    178.9 = c

    260 - 178.9 = T
    81.09 = T

    This was wrong. I subtracted because I thought that in order for there to be no force exerted on the hip, the force would have to be zero, so the combined tensions would have to cancel out the force. Where am I going wrong?
  2. jcsd
  3. Nov 30, 2007 #2
    I forgot to include that the angle for w2 between the string and the horizontal is 40°.
  4. Dec 1, 2007 #3
    You have the figure. But we don't know what the figure is.So either try explaining the situation or attach the diagram. I would prefer the latter.
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