Thread: step-ladder on rough floor

I'd be really grateful for some pointers:

A stepladder is modelled as two model rods OA and AB smoothly hinged at A. The other ends of the rods rest on a rough horizontal floor. The mass of rod AB is 4m, and that of rod OA is m. The angle each rod makes with the vertical is theta. The origin is taken at O with unit vectors >i and^j.

Q. If the angle between OA and OB is steadily increased, determine at which point slipping first occurs if the coefficient of static friction u is the same at O and B.
Is it possible to determine this angle without knowing what the coefficient of static friction is? or is one only able to provide an answer in terms of u, since it is unknown