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Homework Help: Biomechanics Static Forces sled on snowy surface

  1. Sep 15, 2009 #1
    1. The problem statement, all variables and given/known data
    1. A child sits in a sled on a horizontal snowy surface. The combined mass of the child and the sled is 30 kg. The static coefficient of friction is 0.2 and a kinetic coefficient of friction of 0.15. How much force does it take to initiate movement of the sled? (59 N)
    2. Rework #1 for a force oriented at 30 degrees to the horizon. (61N)
    3. Rework #1 for a surface oriented at 10 degrees to the horizon such that the sled is to be pulled up
    the incline. The force is applied to the sled parallel with the surface of the snow. (109 N)

    The answers are given in parenthesis but I can't figure out how to come up with them.
    2. Relevant equations
    force of friction=coefficient of friction*normal force

    3. The attempt at a solution
    #1 is easy and is just equal to 9.8*30*.2 but #2 and #3 i have not been able to get.
  2. jcsd
  3. Sep 16, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Find the normal force by analyzing the force components perpendicular to the surface for each case. Then use the normal force to calculate the friction force.
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