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Calculating the force of friction on an object

  • Thread starter purplecows
  • Start date
  • #1

Homework Statement


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

Homework Equations


µ_s = F_s/ F_n

The Attempt at a Solution


f37784cfe70a77271ef546fefc925dc8.png

So I got 197 N, which was A. However, the answer was B on the answer sheet. What have I done wrong?
 

Answers and Replies

  • #2
rude man
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I think you mean 'coefficient of dynamic friction'.

Your drawing is hard to decipher.
 
  • #3
tiny-tim
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hi purplecows! welcome to pf! :wink:
So I got 197 N, which was A.
so do i :smile:

(are you ok on your other thread?)
 
  • #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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