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SIMPLE force of friction question

  1. Oct 1, 2003 #1
    You are pulling a 15kg wagon by the handle (with 5N of force) forming a 45 degree angle level to the ground. What is the force of friction on the wagon?

    Okay, is it just me, or does this problem seem way to easy to be worth 100 pts?
    It's -3.54N, right? Is the weight of the wagon irrelevant?

  2. jcsd
  3. Oct 2, 2003 #2


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    Staff Emeritus

    To find the fricational force you need to know the coefficient of friction ([mu]). Then the frictional force = [mu] * normal (N) . The normal force is perpendicular to the plane which the object is on and equal to the y component of the weight in your case.

    I can't stress enough how helpful a picture is. Label all the forces and draw their components. Once you are confident that the picture is correct then procede to sum the forces in the x and y and/or z direction, setting the lefthand side to either 0 or m*a.
  4. Oct 2, 2003 #3


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    Staff Emeritus
    Science Advisor

    No, you do not need to know the coefficient of friction or the weight of the bag.

    Assuming that the woman is pulling the bag at a constant speed, the horizontal acceleration is 0 and there must be no net horizontal force. The friction force is exactly the horizontal component of force the woman is applying and oppositely directed.

    I get exactly the same answer you do. Since you are told what the mass of the bag is, you could calculate its weight and then find the coefficient of friction from the information given.
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