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Determine normal force and friction of a toboggan with children

  1. Feb 19, 2005 #1
    I've tried it but I got stuck at the part to find the coefficient of friction.

    A parent pulls a toboggan with three children at a constant velocity for 38m along a horizontal trail. The total mass of the children and the toboggan is 66kg. The force the parent exerts is 58N[18 above the horizontal]

    a)Determine the magnitude of the norml force and the coefficient of kinetic friction.
     
  2. jcsd
  3. Feb 19, 2005 #2
    What have you done so far? What does constant velocity tell you?
     
  4. Feb 19, 2005 #3

    Andrew Mason

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    The horizontal component of the pulling force balances the friction force.

    So:
    [tex]F_{friction} = \mu_kF_N = 58Ncos(18)[/tex]

    All you have to do is work out the normal force. Be careful. There are two components to the parent's pulling force. The vertical component reduces the normal force.

    AM
     
  5. Feb 19, 2005 #4
    Is FRICTION EQUAL TO WORK Facos18 because net f=0?

    and the normal force would be fg=fn=mg?
     
  6. Feb 19, 2005 #5

    Andrew Mason

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    No. See my previous post.

    (1)[tex]F_N = mg - F_{pull}sin(\theta)[/tex]

    (2)[tex]\mu_kF_N = F_{pull}cos(\theta)[/tex]

    Substitute [itex]F_N[/itex] from (1) into (2) to get the coefficient of friction.

    AM
     
  7. Feb 19, 2005 #6
    but why wouldn't fn=fg....doesn't make sense
     
  8. Feb 19, 2005 #7

    Andrew Mason

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    There is an upward lift force due to the angle at which the parent is pulling the toboggan. This lift reduces the downward mg force.

    AM
     
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