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Calculating the force of friction on an object

  1. Nov 2, 2013 #1
    1. The problem statement, all variables and given/known data
    A 40.0-kg object is being pulled along a horizontal surface by means of a rope that exerts a force of 200 N at an angle of 30° below the horizontal. The coefficient of static friction between the object and the surface is 0.40. The force of friction on the object is:
    A) 197 N
    B) 173 N
    C) 392 N
    D) 157 N

    2. Relevant equations
    µ_s = F_s/ F_n

    3. The attempt at a solution
    So I got 197 N, which was A. However, the answer was B on the answer sheet. What have I done wrong?
  2. jcsd
  3. Nov 2, 2013 #2

    rude man

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    I think you mean 'coefficient of dynamic friction'.

    Your drawing is hard to decipher.
  4. Nov 2, 2013 #3


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    hi purplecows! welcome to pf! :wink:
    so do i :smile:

    (are you ok on your other thread?)
  5. Nov 2, 2013 #4

    rude man

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    The answer is B and it's correct.

    There are a lot of red herrings in this problem! I fell for the "static friction" coefficient myself.

    The force is already given, so things like friction coefficients and mass are irrelevant.
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