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Homework Help: Acceleration on an Inclined Plane?

  1. Mar 13, 2010 #1
    1. The problem statement, all variables and given/known data

    A box weighing 20 kg is on an inclined plane with an angle of 30[tex]\circ[/tex].The coefficient of friction is 0.3. What is the acceleration of the box?


    2. Relevant equations

    Newton's Second law ( I think? )

    g= 10 m/s2

    3. The attempt at a solution


    [tex]\sum[/tex]y = 0
    NF - Wysin30[tex]\circ[/tex] = 0
    NF = Wysin30[tex]\circ[/tex]
    NF = [(20)(10)]sin30[tex]\circ[/tex]
    NF = 100 N

    f = [tex]\mu[/tex]NF
    f = (0.3)(100)
    f = 30

    [tex]\sum[/tex]x = ma

    Wcos30[tex]\circ[/tex] + f = m(-a)
    20cos30[tex]\circ[/tex] + 30 = -20a
    [tex]47.32/-20[/tex] = [tex]-20a/-20[/tex]
    a = -2.36 m/s2

    Is this correct? :D
     
  2. jcsd
  3. Mar 13, 2010 #2

    ideasrule

    User Avatar
    Homework Helper

    You have your sines and cosines mixed up. The normal force is Wcos(theta); the parallel force is Wsin(theta).
     
  4. Mar 13, 2010 #3
    so that's the only problem ? :D so If I switched/corrected the two, then my answer would immediately be correct? :D
     
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