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Potential energy of spring and mass system

  1. Nov 16, 2013 #1
    1. The problem statement, all variables and given/known data



    There are 3 equal masses connected by springs with lenght a and spring constant k.

    The system can only move in the x axis.
    x1,x2,x3 is the position of each mass

    What is the potential of the system?

    3. The attempt at a solution

    I came up with this equation:

    [itex] U=\frac{1}{2} k [(a-x2-x1)^2 + (a-x3-x2)^2] [/itex]

    is it right? thanks
    Last edited: Nov 16, 2013
  2. jcsd
  3. Nov 16, 2013 #2


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    Staff: Mentor

    Try x_1 = -100, x_2 = -99, a=1 (in meters if you like). Clearly the spring between 1 and 2 is not stretched (it has rest length 1 and the distance between the points is 1). What does your function give for that spring? Can that be right?
  4. Nov 16, 2013 #3
    [itex] U=\frac{1}{2} k [(x2-x1-a)^2 + (x3-x2-a)^2] [/itex]

    got it
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