# Equilibrium of forces

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1. Jan 16, 2017

### nickyfernandezzz

1. The problem statement, all variables and given/known data
The original question was to find the value of the angle between PA and AB. I have a certain idea regarding how to find it, but first I have to identify all forces acting on the system and their directions. So, I would be grateful if someone can explain how the frictional force acts between PA
and AB.

MY ATTEMPT.
I got a start by marking the forces acting on the system but I can't figure out the direction of frictional force.

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2. Jan 16, 2017

### haruspex

Some verbal statement of the problem would be enlightening.
You have marked mg at point Q, but that does not look like the centre.
I assume you are asking about the direction of the frictional force at A. Generally speaking, you do not need to figure that out in advance. Just assume it is one way along the surface, and if you are wrong it should become obvious (and it might just be a matter of flipping the sign to get the right answer).

3. Jan 16, 2017

### nickyfernandezzz

I'm sorry for not being very clear. Actually, it was stated in the question that Q is the centre of AB.
So, is the friction acting ALONG the surface PA ( either upwards or downwards)?

4. Jan 17, 2017