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Hw help !

  1. Nov 5, 2005 #1
    Hw help plz!

    So the problem begans like this

    A block of mass 8kg is pushed up against a wall by a force P that makes a 50 degree angle with the horizontal. The coefficient of static friction between the block and the wall is 0.249. Determine the possible values for the magnitude of P that allow the block to remain stationary.

    They ask for the miniumum P that will allow the block to remain stationary but I'm not sure how to set it up.

    We know that at Fsmax = UsN, and anything below it is Fs = F . But what exactly is F?

    Fy = Psin50 - Fs - mg

    Since its still stationary Fy is 0

    Does F = Fsmin + mg?

    if so 0 = Psin50 - (Fsmin + mg)

    but when i plug in the values I get the wrong answer still

    can anyone give me some tips? Thanks!
  2. jcsd
  3. Nov 6, 2005 #2


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    Homework Helper

    It sounds to me like you have formulas but don't understand them. You need to understand a formula in relation to the context in which it applies.

    Start by drawing a diagram of all the forces on the block. From that you should be able to deduce a formula to find the answer.

    What are all the forces acting on the block? Assuming the applied force is just enough to ensure the block remains stationary, which forces are pulling the block downwards and which upwards?
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