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Kinetic energy of a spring-mass system

  1. Dec 5, 2009 #1
    1. The problem statement, all variables and given/known data
    The total energy of a spring-mass system oscillating horizontally is 1600 J. What will be the kinetic energy (in joules) of the mass when its displacement is one-fourth of its amplitude?

    2. Relevant equations
    total energy = KE + PE = .5kA2
    KE = .5mv2
    PE = .5kx2

    3. The attempt at a solution
    All I have written down is-
    1600 J = .5kA2

    So, I have no idea how to start solving this problem. Can anyone help me get started? Any help is appreciated!
  2. jcsd
  3. Dec 5, 2009 #2
    At the extreme ends of the displacement, 1/2kx^2=1600 where x is amplitude.

    This leads to 1/2k (.25x)^2 = WHAT WE NEED TO KNOW. Set it up as a proportional problem.

    AS the total energy is 1600J, the KE will be 1600-PE.
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