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Energy and Simple Harmonic Motion

  1. Feb 19, 2009 #1
    1. The problem statement, all variables and given/known data

    A 3.2-kg block is hanging stationary from the end of a vertical spring that is attached to the ceiling. The elastic potential energy of this spring/mass system is 1.8J. What is the elastic potential energy of the system when the 3.2-kg block is replaced by a 5.0-kg block?

    2. Relevant equations

    Elastic potential energy=1/2kx^2
    Gravitational potential energy=mgh

    3. The attempt at a solution
    Help me please!
     
  2. jcsd
  3. Feb 19, 2009 #2

    CompuChip

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    The problem is that you have the extension x of the spring in your formula, which you do not know. However, there is an extra clue in the word "stationary". What does that mean?
     
  4. Feb 19, 2009 #3
    it is not moving, x=0?
     
  5. Feb 19, 2009 #4
    What should I put in for h and k? Thank you, CompuChip!
     
  6. Feb 19, 2009 #5

    CompuChip

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    Exactly, it is not moving. But that does not mean that x = 0 (then the spring would be in its equilibrium position... but it is stretched by the mass that's hanging on it)... it merely says that x is a constant. But what can you say about the net force acting on the block. Which forces are there?
     
  7. Feb 24, 2009 #6
    'x' is the extension from the equilibrium point in the spring when the 3.2kg mass is changed to 5kg. Because 'g' and 'k' stay constant it is just simple ratios....
     
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