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Really Simple Magnitude Question

  1. Sep 29, 2007 #1
    1. The problem statement, all variables and given/known data
    Two crates, A and B, sit at rest side by side on a frictionless horizontal surface. The crates have masses and . A horizontal force is applied to crate A and the two crates move off to the right.

    If the magnitude of force is less than the total weight of the two crates, will it cause the crates to move?



    3. The attempt at a solution

    I already drew the force diagrams for this problem :D with no problems at all.

    Now in this question, I just want to make sure that what I am thinking is correct, as I only get one try.

    If the magnitude of force is less than the total weight of the two crates, then yes it would cause it too move slightly. As the normal force cancels out with the weight force, causing the "rest state".

    At first I was thinking it would not, because the weight force would be bigger than the force of push, but then the force acting from box b to box a would have to be greater than the force applied for it to move.
     
  2. jcsd
  3. Sep 29, 2007 #2

    Doc Al

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    Staff: Mentor

    All you need to start the crates moving is to have an unbalanced force acting on them. The size of the net force doesn't matter. Certainly the vertical forces cancel, but what about horizontal forces?
     
  4. Sep 29, 2007 #3
    so there is an unbalance of forces, since the vertical forces cancel, and there is a unbalance force in the horizontal. So it will move.
     
  5. Sep 29, 2007 #4

    Doc Al

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    Staff: Mentor

    Correct. The only horizontal force is the applied force (there's no friction to oppose it), so the crates will accelerate no matter how small that applied force is.
     
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