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Confusing Problem

  1. Nov 16, 2006 #1

    I did this question one way and realized my answer was totally wrong. Was wondering if anyone knew a possible solution for this problem.

    1. The leg is in the cast in the diagram shown below weight 220N(w1). The leg is held in traction by two weights (w2 and w3) attached to stings and applied as shown in order that there be no force exerted on the hip joint J by the leg in the cast. (In other words, the leg is in translational equilibrium). Weight W3 is 110 N. Calculate the numerical values of w2 and the angle a.

    I am sorry the drawing looks so bad but that was the best I could do using paint.


    Attached Files:

  2. jcsd
  3. Nov 16, 2006 #2

    Chi Meson

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    Despite the fact that this is a leg in traction, this problem is solved exactly as if it were a sign hanging from two cables. You have two unknowns, so you need two equations. One comes from balancing the horizontal componants of the three forces, the other from balancing the vertical componants.
  4. Nov 16, 2006 #3
    im not sure what that means.......could you please explain what u just posted
  5. Nov 16, 2006 #4


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    He is saying that you could cut the leg off the body and the problem would not change. The entire weight of the leg is being supported by the two strings. Notice that in the diagram the point where the strings are attached and where the weight of the leg is acting are the same. This point is the center of mass of the leg. This is necessary so that the leg has no tendency to either rotate or translate. Either of those would put pressure on the hip joint.

    Don't worry about the fact that the object being supported is a leg. Replace it with a block of weight Wl hanging from another string connected at the ppint of intersaection and it will be exactly the same problem as far as the two upper stings are concerned.
  6. Nov 17, 2006 #5
    nice drawing....

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