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Homework Help: Potential energy and conservation

  1. Aug 14, 2012 #1
    1. The problem statement, all variables and given/known data

    A 10.0 kg block is released from point A in Figure P8.57. The track is frictionless except for the portion BC, with a length of 6.00 m. The block travels down the track, hits a spring of force constant k = 2250 N/m, and compresses it 0.300 m from its equilibrium position before coming to rest momentarily. Determine the coefficient of kinetic friction between surface BC and the block.

    image can be found here: http://www.webassign.net/sb5/p8-57.gif

    2. Relevant equations


    3. The attempt at a solution

    initial potential energy - work done by friction = final elastic energy
    Ug - Work by friction = Uel
    mgh - FΔx = (1/2)kx^2
    mgh - μmgΔx = (1/2)kx^2
    μ = [mgh - (1/2)kx^2]/(mgΔx)
    plugging in the numbers…
    μ = [(10 kg)(9.8 m/s^2)(3 m) - .5(2025 N/m)(.3 m)^2]/[(10 kg)(9.8 m/s^2)(6 m)]
    and I got μ= 0.345, but this is incorrect
    and I am not sure why.
    Can someone please help point out my errors?
  2. jcsd
  3. Aug 14, 2012 #2

    Doc Al

    User Avatar

    Staff: Mentor

    This might just be a typo, but you have a different value for k here than earlier.
  4. Aug 14, 2012 #3
    Oops that was the problem! I typed it in wrong when i was making my calculations.
    Thanks so much
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