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Homework Help: Potential Energy

  1. Dec 28, 2006 #1
    1. The problem statement, all variables and given/known data

    A figure is attached.
    A string with length L connects two beads with masses M1,M2.
    what is the equilibrium point?(in terms of the angle theta,as in the figure)

    3. The attempt at a solution

    well I know that I need to find the potential energy as a function of theta,and then find the minimum.

    but I dont know how to express the potential energy in terms of theta

    Attached Files:

  2. jcsd
  3. Dec 28, 2006 #2


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    You know the distance between m1 and m2 is L. To get started, find the distances of m1 and m2 from the rightangle in terms of L and theta.
  4. Dec 28, 2006 #3
    well this is easy

    for m1 : l*cos(theta)
    for m2 : l*sin(theta)

    I can't see how this is helping me
    (by the way,this is not homework,I'm doing extra problems from the book)
  5. Dec 28, 2006 #4


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    The potential energy of a mass = mgh where h is the vertical distance from some point.

    From those lengths, finding the vertical distance of the masses below the right angle (using alpha) is also easy.
  6. Dec 28, 2006 #5
    can't believe I didnt see it..really easy

    thanks :)
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