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Homework Help: Solving problems usng conservation of energy

  1. Oct 9, 2009 #1
    1. The problem statement, all variables and given/known data
    A block of mass 1.5 kg is placed against a horizontal spring of force constant k that is compressed .20 m. the spring is then released and the block travels to the right along a horizontal surface. The coefficient of kinetic friction between the block and the surface is 0.4. After the block has traveled 0.9 m to the right, measured from its initial position against the compressed spring, its velocity is 14.5 m/s. Calculate the force constant k of the spring.

    2. Relevant equations
    Kinetic/gravitational/elastic/friciton (Usage varies for different situations.

    3. The attempt at a solution

    [0+0+Es] Initial = [K+0+0+Ef]

    1/2kv^(2) = 1/2mv^(2) = uNd

    N=fg=mg so this replaces N essentially!

    plugging in...

    1/2k(0)^(2) = 1/2(1.5)(14.5)^(2) + (.4)(1.5)(9.8)(.9)

    k=321 Nt

    Is this correct? Just needing full proof assistance thank you so much.
  2. jcsd
  3. Oct 9, 2009 #2


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    Science Advisor
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    Gold Member

    The method is correct but you need to redo the numbers because they don't agree with mine. What number did you put here (in red)?
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