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Box being pushed up an inclined plane

  1. Dec 9, 2011 #1
    1. The problem statement, all variables and given/known data

    A 250N force is directed horizontally to push a 29kg box up a plane that is inclined at 27 degrees to the horizontal. the box moves up the plane at a constant speed. Determine the magnitude of the normal force, and the coefficient of kinetic friction.
    a(y) = 0m/s

    2. Relevant equations
    F=mg to find the force that is pulling down on it
    Fk= [itex]\mu[/itex] k Fn

    3. The attempt at a solution

    I understand that the forces need to be resolved into the same direction, but i'm not sure what direction the normal force would be pointing in. The force of gravity i got was 284.2N. I can't figure out the kinetic friction until i figure out the normal force.
  2. jcsd
  3. Dec 9, 2011 #2
    The normal force will be at 90 degrees to the inclined surface, and equal and opposite to the component of the weight of the box acting perpendicularly through the plane.
  4. Dec 9, 2011 #3
    maybe i'm resolving my vectors wrong. when i resolve the vector for weight, the part that should be equal and opposite to Fn i'm getting 129.02N which is not possible as it is multiple choice and thats not even one of the answers
  5. Dec 9, 2011 #4
    What are the options you are given?
  6. Dec 9, 2011 #5
    a) 330N 0.31
    b) 310N 0.33
    c) 250N 0.27
    d) 290N 0.30
    e) 370N 0.26

    The answer is e
  7. Dec 9, 2011 #6
    To find the components of the weight, draw an angle formed by the vector of weight and a line perpendicular to and under the surface. This angle is equal to the angle of inclination of the plane.
    Make the x axis parallel to the surface, so the y axis would be perpendicular to the surface and parallel to the normal force.
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