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Homework Help: I have no clue what the normal force is :-(

  1. Sep 23, 2008 #1
    An adult is pulling two small children in sleigh over level snow. The sleigh and the children have a total mass of 47 kg. The sleigh rope makes an angle of 23 with the horizontal, The coefficient of kinetic friction between the sleigh and the snow is 0.11. Calculate the magnitude of the tension in the rope needed to keep the sleigh moving at constant speed.

    The book gives me a hint saying that the normal force is not equal in magnitude of the gravity.

    I don't get why they are not equal...because the sleigh is still on a leveled surface... so why is not same as Fg? And how do i figure out the normal force?
  2. jcsd
  3. Sep 23, 2008 #2
    That was a pretty stupid hint for the book to give, so I'm going to assume that you read the question incorrectly or mistyped. Say, the book says the normal force is not equal in magnitude to the weight. That makes sense (so did the other hint, but it was unnecessary).

    You have to account for the upwards force of the slanted pull.
    Fp(vector) = Fp(cos)~ x-direction + Fp(sin)~ y-direction
    where Fp=force of pull and ~=angle with respect to the horizontal

    So, Fw (weight vector) is equal in magnitude to the combined magnitudes of Fn (normal force) and Fp(sin)~
    Fw - [Fn + Fp(sin)~] = 0 N
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