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Pulling a sled - find friction & force exerted on puller

  1. Oct 5, 2008 #1
    1. A child pulls a sled with mass 9.0kg through the snow(note: no coefficient of friction given, but there _is_ friction between sled & snow). The sled accelerates at 1.0 m/s2. The rope exerts 27Nt on the sled in the forward direction.

    a) what force must the rope exert on the child (magnitude & direction)?

    b) What is the magnitude of the frictional force on the sled (hint: it's in the opposite direction of the sled's motion)?





    2. Relevant equations

    F=ma

    3. The attempt at a solution

    a) 27 Nt, due to Newton's 3rd law, in the opposite direction of the child/sled's motion.


    b)
    Frope - Fk = Ftotal = ma

    Frope = Fk + ma

    27 = Fk + (9 * 1)

    18Nt = Fk


    are my answers correct? Should their signs be negative, because they are in the opposite direction of the sled's motion? Have I made any glaring omissions regarding the rope's tension?
     
  2. jcsd
  3. Oct 5, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good to me. Magnitudes are always positive. (The abbreviation for Newton is N, not Nt.)
     
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