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Energy in a Spring Question

  1. Oct 15, 2007 #1
    1. The problem statement, all variables and given/known data
    A .3 kg mass rest on top of a spring that has been compressed by .04 m. Neglect any frictional effects, and consider the spring to be massless. Then, if the spring has a constant k equal to 2000 n/m, to what height will the mass rise when the system is released.


    2. Relevant equations

    PE(spring)= (1/2)kx^2

    KE= 1/2mv^2


    3. The attempt at a solution

    I got the PE in the system to be 1.6 J. Im not sure how this would translate into a vertical height. Thanks in advance!
     
    Last edited: Oct 15, 2007
  2. jcsd
  3. Oct 15, 2007 #2

    Doc Al

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    Staff: Mentor

    How did you arrive at this?

    Consider gravitational PE.
     
  4. Oct 15, 2007 #3
    I messed up, used PE=1/2kmx^2 for some reason. I got 1.6 J.

    And in Grav. PE, the H should be the same as the H Im looking for so PE(grav)=PE(Spring).
    Or maybe Im missing something.
     
  5. Oct 15, 2007 #4
    Ok I got .54 m when i put Pe(grave)=Pe(spring). Thats an answer choice! Is this correct?
     
  6. Oct 15, 2007 #5

    Doc Al

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    It depends on what the height is being measured with respect to. The initial position on top of the spring? Or the compressed position?
     
  7. Oct 15, 2007 #6
    I suppose its the top of the spring
     
  8. Oct 15, 2007 #7

    Doc Al

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    Staff: Mentor

    That's what I would say. :wink:
     
  9. Oct 15, 2007 #8
    Thank you!
     
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