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Homework Help: Spring Constant

  1. Aug 12, 2009 #1
    A .20- kg mass attached to a spring is pulled back horizontally across a table so that the potential energy of the system is increased from zero to 120 J. Ignoring friction, what is the kinetic energy of the system after the mass is released and has moved to a point where the potential energy has decreased to 80 J.

    PE= 1/2 k*x^2
    KE= 1/2 m*v^2
    F= -kx

    How would I find the spring constant or PE without the distance of the spring?
  2. jcsd
  3. Aug 12, 2009 #2


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    Homework Helper

    What is the change in potential energy converted into?
  4. Aug 12, 2009 #3
    Consider the following:
    All the forces in the system are conservative.

    What fundamental quantity is conserved?
  5. Aug 12, 2009 #4


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    You are told what the potential energy is at each point, so you don't need to know how it was calculated. Just write down the total energy at each point in the most general terms possible, and go from there.
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