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Homework Help: Newton's Laws Finding Applied Force and other Forces

  1. Mar 29, 2012 #1
    1. Sean the skier is headed for a rough patch of snow with the coeffcient of friction 0.20. Find his acceleration if his mass is 50 kg.

    2. F=ma, coeffcient of friction=Ff/Fn

    3. Fgravity = 490.5 using the equation coeffcient of friction=Ff/Fn we get 0.20 = Ff/490.5 which equals Ff = 98.1
    This is where i get stuck. i do not know how to find the Force applied to use it to find the sum of the two forces (force applied and force of friction) to plug into the equation F= ma.
  2. jcsd
  3. Mar 29, 2012 #2
    The sum of forces equals ma (Newtons 2nd law). Use it to write down the equation(s) to be solved.
    You know that the vertical acceleation is zero:
    [itex]0= N - mg\\
    F_{fric} = \mu N=\mu mg\\
    \sum F_{horizontal} = ma = -F_{fric}[/itex]
    So never plug into any equation unless you have a good reason
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