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Homework Help: Surprising static equilibrium

  1. Feb 21, 2010 #1
    1. The problem statement, all variables and given/known data

    Consider the situation of the figure, where a string of negligible mass and length L is fixed at two points A and B, with B dislocated of A by a distance w(<L) and vertically dislocated by a distance h < sqrt(L^2-w^2) A mass is hung on the rope using a moving pulley of negligible mass. The pulley has no friction and can move freely along the rope until it "finds" the position of equilibrium in which the pulley is at a horizontal distance x of point A, and a vertical distance y of that point.


    What are the equilibrium angles Theta(1) and Theta(2)?
    What are the values of x, y , L1 and L2 at equilibrium?

    2. Relevant equations

    There aren't any besides the fact that the potential energy must be a minimum

    3. The attempt at a solution

    I can't even get started.
  2. jcsd
  3. Feb 21, 2010 #2


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    I haven't looked at this problem in any detail, but it seems that there are enough equilibrium equations, and given geometry, to solve it. You should probably start by drawing a free body diagram of the hanging mass, and writing the 2 equilibrium equations using Newton's 1st law. Note that ideal pulleys change the direction of the tension in the cable, but not its magnitude. Then you've got to do some trig work.
  4. Feb 21, 2010 #3
    Thanks for the reply, but my problems is in the trig work. I don't know how to get started
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