# Homework Help: Friction, Statics, Finding maximum angle and minimum coefficient of friction

1. Nov 22, 2011

### papasmurf

1. The problem statement, all variables and given/known data
If the coefficient of static friction at B is μs = 0.3, determine the largest angle
θ, and the minimum coefficient of static friction at A, so that the roller remains self-
locking, regardless of the magnitude of the force P applied to the belt. Neglect the weight
of the roller and neglect friction between belt and vertical surface.

2. Relevant equations
ƩM=0
ƩFx=0
ƩFy=0
FAANA
FBBNB=0.3NB

3. The attempt at a solution
I have attempted the solution quite a few times a couple of different ways. I keep getting stuck with variables that I can't solve for, so I have come to the conclusion that I am probably not going about it the right way. My first attempt, I took the moment about A, and then summed up the forces in the x and y directions, but wound up not being able to solve for θ or μA. I attached an attempt at a free body diagram, perhaps I don't have the friction forces going in the right direction? I would appreciate any help!

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