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Homework Help: Work Energy: block w/ friction

  1. Dec 15, 2009 #1
    1. The problem statement, all variables and given/known data
    Find the initial speed of a block which travels 10m along a horizontal surface if [tex]\mu[/tex]= 0.40 between the block and the surface before stopping.

    2. Relevant equations
    [tex]\Sigma[/tex]W = 1/2mvB2 - 1/2mvA2 + mgyB - mgyA

    [tex]\Sigma[/tex]W = W * dAB * cos (W, dAB)

    f = [tex]\mu[/tex]* N
    N= mgsin[tex]\theta[/tex]

    3. The attempt at a solution
    so far i have:
    [tex]\Sigma[/tex]W = 0
    [tex]\Sigma[/tex]W = WN + WW + Wf


    [tex]\Sigma[/tex]W = WW * dAB * cos (270)
    [tex]\Sigma[/tex]W = WW * 10m * 0

    not sure if i'm doing this right or where to go from here
  2. jcsd
  3. Dec 15, 2009 #2
    This problem requires an equation that you haven't included yet.

    So we'll start with:
    [tex]\Sigma[/tex]F = max
    [tex]\Sigma[/tex]F = Px + fx + Nx + Wx
    max = Px + fx+ Nx + Wx

    [tex]\mu[/tex] = -a / g
    Try to solve it from here.
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