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Spring and Gravity Potential Energies

  1. Nov 12, 2007 #1
    1. The problem statement, all variables and given/known data
    A 2-kg block is dropped from a height of 0.4 m onto a spring force whose constant k is 1960 N/m. Find the maximum distance the spring will be compressed.


    2. Relevant equations
    U1+K1=U2+K2


    3. The attempt at a solution
    both the initial and final kinetic energy should be 0 so we should get an equation like this:
    mgh=(1/2)kx^2+mg(value)

    I can't find an expression to put in for value that only has x and no other unknown variables.
     
  2. jcsd
  3. Nov 12, 2007 #2

    G01

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    The expression you have will work.

    Hint: Let the lowest point the block reaches be h=0m.
     
  4. Nov 12, 2007 #3
    so I would substitute 0 in for value to get x = .089 m, correct? Yeah, that's what I have been getting. However, my teacher told me the answer is 1.00 m. I am starting to wonder if he read off the wrong answer. Do you get .089 m too?
     
  5. Nov 12, 2007 #4

    G01

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    I also get .089m. Check to make sure your numbers and units are correct. If they are, then I suggest talking to your teacher about it. Even teachers aren't perfect!:smile:

    Technically, the method we are using assumed the spring is compressed a negligible amount, but I think this is a reasonable assumption that wouldn't change the answer that much.
     
    Last edited: Nov 12, 2007
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