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Force of Friction Formula?

  1. Jul 9, 2011 #1
    For the question: A 435 n box is sliding down a 40.00 inclined. If the acceleration of the box is 0.250m/s2. Which formula would I use to find just the force of friction? and would I change the Newtons to kilograms?
  2. jcsd
  3. Jul 10, 2011 #2
    The mass of the box is m = Fw/g = 435n / 9.81 m/s2 = 44.3 kg.
    Is it 40 degrees?
    The parallel force Fp = Fw(sin40) = 280n
    The net unbalanced force responsible for acceleration is F = m a = 44.3kg (0.25m/s/s) = 11.1n.
    If Ff = |Fp| then the box would not accelerate.
    The Force of friction, Ff = 280n - 11.1n = 268.9n I think, but correct me if I am wrong.
  4. Jul 11, 2011 #3
    Well, the answer is supposed to be 10 but I think there was probably a typo. :)
    thanks so much for your help!
    and yes, it was supposed to be 40.0 degrees. :)
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