Calculating the force of friction on an object

AI Thread Summary
A 40.0-kg object is being pulled with a 200 N force at a 30° angle, and the coefficient of static friction is 0.40. The calculated force of friction was initially thought to be 197 N, but the correct answer is 173 N. The confusion arises from misinterpreting the type of friction involved, as the problem includes red herrings. Understanding the dynamics of the situation is crucial for accurate calculations.
purplecows
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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?
 
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I think you mean 'coefficient of dynamic friction'.

Your drawing is hard to decipher.
 
hi purplecows! welcome to pf! :wink:
purplecows said:
So I got 197 N, which was A.

so do i :smile:

(are you ok on your other thread?)
 
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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Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
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