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Homework Help: Energy and Friction in a block

  1. May 5, 2017 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    The block has potential energy U at the top of the ramp, and this is transfered to kinetic energy K at the bottom, which is then trasnfered to work done by friction, Wfr.
    U = K Conservation of energy
    K = Wfr Conservation of energy
    g = 10 m/s2

    3. The attempt at a solution
    U = mgh = 3*45*10 = 1350 J
    1350 J = Wfr = Ffr * d = m*g*u*d = 3*10*1*d
    1350 = 30*d
    d = 45 m

    This does not match the answers. Am I doing anything wrong?
  2. jcsd
  3. May 5, 2017 #2


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    Staff: Mentor

    Your calculations are correct. There is likely an error in the problem statement. I suspect that they intended the coefficient of kinetic friction to be 0.1. Your answer of 45 m is correct for the given information.
  4. May 5, 2017 #3
    That is a very good point. We usually don't see coefficients of friction to be 1.0, so it probably was 0.1. I just wanted to make sure my understanding of work-energy relationship was correct. Thanks!
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