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Conservation of Energy please help

  1. Oct 13, 2009 #1
    Conservation of Energy please help!!

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

    An 840 kg roller coaster car is launched from a giant spring of constant k=31kN/m into a frictionless loop-the-loop track of radius 6.2m, what is the minimum amount that the spring must be compressed if the car is to stay on the track?

    2. Relevant equations

    v=n+mg = (mv^2)/r
    v= √(gr)

    mgh=0.5mv^2

    3. The attempt at a solution

    mgh=0.5mv^2
    mgh=0.5m √(gr)^2
    mgh=0.5mgr
    h = 0.5r
    h= 3.1 m

    and im stuck after this... please help...
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    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. Oct 13, 2009 #2
    Re: Conservation of Energy please help!!

    Your velocity is correct.

    It has initial energy which should be equal to the energy at the top point of the loop (what energies are present here?).
    Find it's initial energy and set that equal to its final energy.
     
  4. Oct 13, 2009 #3
    Re: Conservation of Energy please help!!

    the initial energy is the potential energy right??
     
  5. Oct 13, 2009 #4
    Re: Conservation of Energy please help!!

    Yes and then there are two energies present at the top of the loop.
     
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