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Frictional Forces Problem

  1. Dec 13, 2011 #1
    1. The problem statement, all variables and given/known data

    A force of 400 newtons is applied horizontally to a box. The kinetic coefficient of friction is .64 and the acceleration of the box is 4 m/s^2. Find the mass and the force of friction.

    2. Relevant equations
    assume that acceleration due to gravity or g=10 m/s^2

    3. The attempt at a solution
    please explain!!
  2. jcsd
  3. Dec 13, 2011 #2

    Simon Bridge

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    Welcome to PF.
    Did you draw the free-body diagram?

    There should be four forces on it.
    Are the forces balanced?
    Are any of them related to each other?
  4. Dec 13, 2011 #3
    yeah i drew the free body diagram and have that there are four forces but im having trouble finding the normal force without knowing the mass since i need it to find the force of fricition
  5. Dec 13, 2011 #4

    Simon Bridge

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    Write everything out as symbols - use algebra to get an equation that says "m=" a bunch of symbols. Then put the numbers in.
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