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Homework Help: Analyzing motion with friction

  1. Apr 18, 2010 #1
    A 12kg toboggan is pulled along at a constant velocity on a horizontal surface by a horizontal force of 11N.
    a) What is the force of gravity on the toboggan?
    b) What is the coefficient of friction?
    c) How much horizontal force is needed to pull the toboggan at a constant velocity if two 57kg girls are sitting in it?

    m=12kg
    FA= 11N

    a) Fg=FN
    mg=FN
    12(9.8)=FN
    118N=FN=Fg

    Fg=118N

    b) FA=Ff; constant vel.
    FK=FA=11N

    Fk=μKFN
    11N= μK(118N)
    μK=11N/118N
    μK=0.093

    c)m= 12kg + 2(57kg)= 126kg

    Fg=FN
    mg=FN
    126(9.8)=FN
    1234.8N=FN


    m=126kg
    FN=1234.8N
    FK=FA=?
    im stuck here..
     
  2. jcsd
  3. Apr 18, 2010 #2
    You have the coefficient of friction from part b. You can use this value to find the force of kinetic friction acting on the toboggan+kids.

    And because the tobaggon must move at a constant velocity, the net force must be zero. Thus, like you wrote, Fa = Fk.
     
  4. Apr 18, 2010 #3
    omg i feel stupid now :|
    thanks lol
     
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