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Homework Help: Forces on an Incline

  1. Sep 30, 2007 #1


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    1. The problem statement, all variables and given/known data

    The 3.91 kg physics book shown is connected by a string to a 519.0 g coffee cup. The book is given a push up the slope and released with a speed of 3.99 m/s. The coefficients of friction are μs = 0.457 and μk = 0.330. What is the acceleration of the book if the slope is inclined at 21.7°?

    2. Relevant equations


    3. The attempt at a solution

    I've tried splitting the equation into two: the book and the coffee mug.


    [tex]F_N_E_T=\vec{F}_g - \vec{F}_T[/tex]
    [tex]ma=mg - T[/tex]


    I've split weight into its x and y components.

    [tex]F_N_E_T = T + W_x - F_k_i_n_e_t_i_c[/tex]
    [tex]ma = T + W_x - F_k_i_n_e_t_i_c[/tex]
    [tex]3.91a = T + 8.152[/tex]
    [tex]T = 3.91a - 8.152[/tex]

    Then I equated T and solved for a. But I'm still getting the wrong answer...
  2. jcsd
  3. Sep 30, 2007 #2


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    Homework Helper

    can you describe how you got the 8.152N?
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