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Normal Force and Coefficient of kinetic friction (Quiz 4, q15)

  1. Aug 30, 2014 #1
    A 250-N force is directed horizontally as shown to push a 29-kg box up an inclined plane at a constant speed. Determine the magnitude of the normal force, FN, and the coefficient of kinetic friction, µk.
    FN µk
    (a) 330 N 0.31
    (b) 310 N 0.33
    (c) 250 N 0.27
    (d) 290 N 0.30
    (e) 370 N 0.26

    My attempt:

    I know FN = mg
    so FN = (29kg) (9.8 m/s^2)
    FN = 284

    why is it not right?

    Attached Files:

  2. jcsd
  3. Aug 30, 2014 #2


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    Gold Member

    From the diagram and equations you've provided, it doesn't appear that you've accounted for the angle of the incline. Try to account for that.
  4. Aug 30, 2014 #3
    ok FN = Mg
    = 250N sin 27
    = 113

    still not the right answer
  5. Aug 30, 2014 #4


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    Science Advisor
    Homework Helper
    Gold Member

    That's not the only omission.
    gcombina, choose two directions, e.g. vertical and horizontal. In each direction, list all the forces that act in that direction. What two equations can you write?
    (if you prefer, you can choose parallel to the plane and normal to the plane, or horizontal and normal to the plane, whatever.)
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