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Homework Help: Friction angeled surace

  1. Jul 11, 2011 #1
    1. The problem statement, all variables and given/known data
    A box is placed on an angeled surface.

    m = 15 kg
    f = 0,3

    [PLAIN]http://img5.imageshack.us/img5/8717/friction.png [Broken]

    Will the box slip downwards if X = 0?

    How big does the force X have to be to push th box upwards?

    2. Relevant equations

    3. The attempt at a solution
    My idea was that the only force working upwards is Ff.

    A = 55°
    g = 9,81
    N = mg*cos(90-35)+18 = 102,40 N

    Ff = 0,3*N = 30,72

    Force downwards: mgcos35-18 = 102,54 N

    The force down is greater than Ff therefore it would slip if X = 0.

    To get how big X needs to be to make the box move up i simply subtracted the force down with Ff and got = 71,82 N.

    Could this possibly be correct?
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jul 11, 2011 #2
    Why is your downward force mgcos(35)-18? It should just be mgcos(35)
  4. Jul 12, 2011 #3

    Yea, okey. So the rest would be correct then?
  5. Jul 12, 2011 #4
    After changing the value of the downward force, yes.
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