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Finding out applied force in order to get acceleration

  1. Jan 28, 2012 #1
    1. The problem statement, all variables and given/known data
    A person pushes a box across a horizontal floor with an initial velocity of 5.2m/s. The box has a mass of 22kg, and the coefficient of Kinetic friction between the box and the floor is 0.44. How far does the box slide before coming to rest?

    2. Relevant equations
    μk = FK/FN
    Fnetx = FA - FK(assuming that right is positive and left is negative)
    V2 - V1 = 2aΔd

    3. The attempt at a solution
    Rearrange μk = FK/FN to FK = μkFN
    Find Normal Force
    FN = FG
    FG = mg
    Get 215.6 for FG which is in turn the normal force.
    FK = (0.44)(215.6)
    FK = 94.9
    Find acceleration
    Fnet = FA - FK
    ma = FA - FK

    And at this point I do not know what to do as I do not have the apllied force.
    The plan after that was to rearrange the Kinematic equation into Δd = V2-V1/2a and fill in for that.
    Unless of course my Free Body Diagram is wrong and there IS no applied force, although that seems unlikely.
  2. jcsd
  3. Jan 28, 2012 #2
    Based on my reading of this problem it seems that the correct answer is the one that you hit on at the end, that there is no applied force in this problem.
  4. Jan 28, 2012 #3


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    Homework Helper

    Hi DPXJube,

    How about we try conservation of energy since your usual method is not working :wink:

    The change in kinetic energy = work done by the frictional force.
  5. Jan 28, 2012 #4
    Unfortunately I've checked the answer for the question and there is indeed an applied force.
  6. Jan 28, 2012 #5


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    Homework Helper

    In that case, your question cannot be solved. What was the answer given?
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