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Homework Help: Elephant in the way kinetic energy problem.

  1. Oct 10, 2007 #1
    "Elephant in the way" kinetic energy problem.

    1. The problem statement, all variables and given/known data

    I found this on one of those "OMG FUNNY" internet web pages. I am trying to attempt a solution.

    2. Relevant equations

    Mechanical energy is conserved so Einitial=Efinal. Uinitial+Kinitial=Ufinal+Kfinal.

    3. The attempt at a solution

    KE+PE = Total Energy. When the 3kg object is released from a 5m. I am unsure on how to procede with this problem. How does the force constant k of the spring factor into the solution?
    Last edited: Oct 10, 2007
  2. jcsd
  3. Jun 10, 2008 #2
    You're doing it wrong.
    How to do this problem:
    U(initial) {which is gravitational potential energy} = mgh, where h is 5m, m is 3kg, g is 9.81m/s^2.
    U(final) {which is elastic potential energy} = 1/2kx^2, where k is 100.
    WE WANT X.
    W=delta E
    Conservation of energy in sys mass, plane, earth. W=0
    0=1/2kx^2 - mgh
    So, x=Square Root ((2mgh)/k)
    So, the answer in this problem is SqRt((2(3kg)(9.81m/s^2)(5m))/100)
    ~SqRt 3 = 1.73205 meters

    Hope that helped, if you care at this point, months later.
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