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Homework Help: Acceleration with force of gravity and friction

  1. Jul 17, 2011 #1
    1. The problem statement, all variables and given/known data

    A block is placed against the vertical front of a cart. The coefficient of static frction between the block and the cart is [itex]\mu[/itex]s. What acceleration must the cart have in order that the block does not fall? How would an observer on the cart describe the behavior of the block?


    2. Relevant equations
    F=[itex]\mu[/itex]s*n
    F=ma



    3. The attempt at a solution
    I have no idea how to start this problem. I know that the force pushing up on the block is equal to mg. I tried drawing acceleration as a horizontal vector, then setting a=mg, then trying to solve, but that didn't quite work out..
     
  2. jcsd
  3. Jul 17, 2011 #2

    Doc Al

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    Staff: Mentor

    Good. What other forces act on the block?
    'mg' is a force, which can't be set equal to an acceleration.

    Identify all the forces and apply Newton's 2nd law.
     
  4. Jul 17, 2011 #3
    so after trying a few things, i got[itex]\mu[/itex]s /g for my answer. I think that should be right.
     
  5. Jul 17, 2011 #4

    Doc Al

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    Staff: Mentor

    Almost. :wink:
     
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