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Pushing a box (forces)

  1. Nov 28, 2007 #1
    1. The problem statement, all variables and given/known data
    You exert a constant horizontal force on a large box. As a result the box moves across a horizontal floor at a constant speed v0.

    If you double the constant horizontal force on the box, how would the box then move?


    2. Relevant equations
    F = ma = m dv/dt


    3. The attempt at a solution
    Well, this question is a tad confusing to me, if the box is moving at a constant speed v0 then I have to assume that I would just push the box for an instant & then get it to move at a constant v0.

    If I were to double the force, then I would think that the speed would then be 2v0, however this is not the case... (dv/dt is proportional to F)

    Can anyone explain how to determine the motion?
     
  2. jcsd
  3. Nov 28, 2007 #2

    Doc Al

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    Staff: Mentor

    You are misinterpreting the problem. The only reason the box continues moving at constant speed is because you keep pushing with the constant horizontal force. Hint: What's the net force acting on the box? What other force must be acting on the box?
     
  4. Nov 28, 2007 #3
    Thanks for your reply



    Alright so if I draw a free body diagram and add in friction I can see
    ma = F - Ff
    Since the velocity is constant a = 0 so
    F = Ff

    So if I double F to 2F, then it's accelerating?
    2F - Ff = ma
    F = ma
    a = F/m ?
     
    Last edited: Nov 28, 2007
  5. Nov 28, 2007 #4

    Doc Al

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    Staff: Mentor

    Very good!
     
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