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Homework Help: PE of weight on a spring

  1. Apr 29, 2012 #1
    1. The problem statement, all variables and given/known data
    A spring of length 75cm has a mass of 0.5kg hanging from it.
    If the spring constant = 40N/m calculate:
    a) the extension of the spring
    b) The change in PE of the mass


    2. Relevant equations
    Part (a) is easy x = (0.5 x 9.81)/40 = 0.123m
    Part (b) energy = 0.5kx^2 gives 0.30J which is WRONG !!!!

    WHY ?????


    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 29, 2012 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi Emilyjoint! :smile:
    that's the energy of the spring

    (energy is not conserved … if you released the mass from rest, it would sail through that equilibrium position at high speed, wouldn't it? :wink:)
     
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