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Homework Help: A block collides with a horizontal spring

  1. Feb 22, 2008 #1
    1. The problem statement, all variables and given/known data
    A moving 2.7 kg block collides with a horizontal spring whose spring constant is 356 N/m.

    The block compresses the spring a maximum distance of 13.0 cm from its rest postion. The coefficient of kinetic friction between the block and the horizontal surface is 0.24. What is the work done by the spring in bringing the block to rest?

    2. Relevant equations
    f_k=mu_k * n

    3. The attempt at a solution

    F= 356 N * .13 m = 46.28 N, so the box exerts 46.28 N on the spring.

    The force from friction is .24 * 2.7 kg * 9.80 m/s = 6.35.

    From here I am unsure of where to go. I was under the impression that I'd simple multiply 46.28 N * .13 m, but that isn't giving me the correct answer. Do I need to also subtract the work done by friction? I had assumed that was taken into account by removing the 6.35. Input would be greatly appreciated.

    Edit: Am I simply getting it wrong because I'm not putting in a negative sign?
    Last edited: Feb 23, 2008
  2. jcsd
  3. Feb 23, 2008 #2
    Use energies ...
    See the work related equations:
    W = Fd
    W = change in U
    Us = 0.5kx^2 ....
  4. Feb 23, 2008 #3
    So, Us= 3.0 = W?
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