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Find acc. given coefficient of frict. on incline slope

  1. Nov 11, 2009 #1
    1. The problem statement, all

    variables and given/known data

    A clerk moves a box of cans down an

    aisle by pulling on a strap attached to

    the box. The clerk pulls with a force

    of 190.0 N at an angle of 28° with the

    horizontal. The box has a mass of 37

    kg, and the coefficient of kinetic

    friction between the box and the floor

    is 0.45. Find the acceleration of the

    box.


    2. Relevant equations
    Ff=U*Fn



    3. The attempt at a solution
    I tried solving this three times. I

    found x and y components:
    X:167.8N
    Y:89.2N

    Tried to find the Fn:
    cos(28)89.2= 78.8N

    Ff=.45(78.8)
    Ff=35.5N
    Fa=190-35.5N= 154.6N

    154.6N=37a
    a=4.2N

    I also tried subtracting the force

    parallel by the force applied and got

    the wrong acceleration also. Am I

    finding the Force Normal wrong? Some

    direction would be great thanks.
     
  2. jcsd
  3. Nov 12, 2009 #2
    anyone know what i'm doing wrong here?
     
  4. Nov 12, 2009 #3

    hage567

    User Avatar
    Homework Helper

    OK, this is fine.
    This is not correct. Are you trying to find your normal force based on the applied force?

    You have forgotten to include the weight of the box anywhere in your calculation.

    The normal force will be the difference between the weight of the box and the component of the applied force in the vertical direction. When doing problems like this, you must consider all forces in each direction. Make sure to start by drawing a diagram with all of the forces showing. Then sum them up in each direction, to get your equations.
     
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