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Homework Help: Properties of Friction

  1. Feb 15, 2010 #1
    1. The problem statement, all variables and given/known data
    Body A weighs 110 N, and body B weighs 37 N. The coefficients of friction between A and the incline are μs = 0.56 and μk = 0.25. Angle θ is 40°. Let the positive direction of an x axis be up the incline.


    (a). Find the acceleration of A if A is initially at rest.
    (........ m/s^2) i

    (b). Find the acceleration of A if A is moving up the incline.
    (.........m/s^2) i

    (c). Find the acceleration of A if A is moving down the incline.
    (.........m/s^2) i

    2. Relevant equations

    3. The attempt at a solution
    So I am not really sure how to solve this problem at all. I have tried a few ways, none have come up with reasonable or correct answers.

    I tried using...

    FT = mA * g * sin(theta) - fk

    where fk = mewk * FN
    and setting FN = g * a

    I then solved for a and came out with 134 but that was wrong and didn't make sense.

    I have no idea what to do next. Can anyone help me out? That would be awsome.

    Attached Files:

  2. jcsd
  3. Feb 15, 2010 #2
    So I got part (a). which is 0. I don't know why I didn't try that before. I feel stupid. But parts (b). and (c). I am still not sure about.
  4. Feb 16, 2010 #3


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    Science Advisor
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    Gold Member

    This problem makes no sense. Either the block A is at rest, or it moves up the plane, or moves down the plane. It can't do all three!
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