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Help please. (Work & Force)

  1. Dec 3, 2003 #1
    I've been stuck on this problem for two hours and my teacher hasn't taught properly.

    A parent pulls a toboggan with three children at a constant velocity for 38 m along a horizontal snow-covered trail. The total mass of the children and the toboggan is 66 kg. The force the parent exerts is 58 N [18 degrees above the horizontal].
    a) Determine the magnitude of the normal force and the coefficient of the kinetic fiction.
    b) Determine the work done on the toboggan by kniectic friction.
    c) List three forces, or components of forces, that do zero work on the toboggan.
    d) How much work does the parent do on the toboggan in pulling it the first 25m?

    This is what I have gotten so far:
    a) Fn = mg = 66*9.8 N
    c) Fn, Fg, Fa of the children on the tobaggan
    d) W = F*d*cos theta = 58*38*cos 18 = 2096.13 N
    Is the above correct?

    For part a, I don't understand how to solve for the coefficient. I only know of the formula, uk = Fk / Fn, but I don't think I have Fk?

    Thanks for the help in advance, much appreciated.
  2. jcsd
  3. Dec 3, 2003 #2
    A constant velocity means that the forces on the sled are balanced. (Newton's first law) That thus means that the force the parents exert on the sled = frictional force pushing the sled back. Thus,

    Fk(frictional force) = force the parents exert on sled (or 58 * cos18)
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