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Homework Help: Spring and Block

  1. May 12, 2008 #1

    grouchy

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    [SOLVED] Spring and Block

    A spring is compressed 6 cm and an 6 kg block is placed against it. when the spring is released the block shoots forward along a rough, horizontal surface traveling 1.2 m before coming to a stop. The coefficient of kinetic friction between the block and the surface is 0.4. Find the speed acquired by the block as it leaves the spring.




    I try to use conservation of energy but I'm having trouble since I'm not given k or v (find k would be the second question).
     
    grouchy, May 12, 2008
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  3. May 12, 2008 #2

    Doc Al

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    Staff: Mentor

    Although the problem does not make it clear, let's assume that the 1.2 m does not include the 6 cm that the spring expands. Further, assume that the rough surface only begins after the spring has expanded.

    The block leaves the spring with some speed. What happens to its KE? How much work is done by friction?
     
    Doc Al, May 12, 2008
  4. May 12, 2008 #3

    grouchy

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    GOT it, I kept assuming that I need to use the potential of the spring. All i need was..

    1/2mv^2 = k(coefficient of kinetic friction)Nd
    v = square root of (2kNd/m) = 3.07 m/s matches up perfect

    Also, I used the 1.2 m for d.

    thx.
     
    Last edited: May 12, 2008
    grouchy, May 12, 2008
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