# Calculating the force of friction on an object

1. Nov 2, 2013

### purplecows

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. Nov 2, 2013

### rude man

I think you mean 'coefficient of dynamic friction'.

Your drawing is hard to decipher.

3. Nov 2, 2013

### tiny-tim

hi purplecows! welcome to pf!
so do i

4. Nov 2, 2013

### rude man

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.