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Homework Help: Box and Spring Question

  1. May 28, 2007 #1
    In Figure 8-34, a 1.2 kg block is held at rest against a spring with a force constant k = 670 N/m. Initially, the spring is compressed a distance d. When the block is released, it slides across a surface that is frictionless, except for a rough patch of width 5.0 cm that has a coefficient of kinetic friction ┬Ák = 0.44. Find d such that the block's speed after crossing the rough patch is 1.6 m/s.



    onservation of energy:

    energy stored in spring = final kinetic energy + energy taken by friction (work)

    (1/2) k d2 = (1/2) m v2 - u m g d


    or (1/2) * 670 * d2 = (1/2) * 1.2 * 1.62 - 0.44 * 1.2 * 9.8 * 0.05

    335 * d2 = 1.536 - 0.259 = 1.277

    d2 = 1.277/335 = 0.003812 so d = 0.0617 meters or 6.17 cm

    Cannot figure out what I am missing here....
     
  2. jcsd
  3. May 28, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Correct.

    Incorrect.
     
  4. May 28, 2007 #3
    A simple sign error lol....Thansk so much...would have hated to lose points after doing all the real work correctly lol
     
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