Static equilibrium of a window washer

[TN17]

I was given 2 problems based on statics and I was wondering if anyone could help.
Thank you - we just learned the concepts of statics TODAY and were given an assignment immediately, so any help would be appreciated.



A window washer attempts to lean a ladder against a frictionless wall. He finds that the ladder slips on the ground when it is placed at an angle of less than 75◦ to the ground but remains in place when the angle is greater than 75◦. Find the coefficient of static friction between the ladder and the ground


I know that:
To be static, Torque - F(r)sinthetha and that Torque(net) = 0
Coefficient of static friction = F(friction) / Normal
I think I might have to split it into components...

AND

Estimate the magnitude of the force F an average person must apply to a wheelchair’s main wheel to roll up over a sidewalk curb. This main wheel, which is the one that comes in contact with the curb, has a radius r, and the height of the curb is h.

I always have trouble with estimation problems. I don't know where to begin.

 

[ehild]

First thing: make a drawing: the ladder with the ground and the wall for the first problem and slope and wheelchair for the second problem. Find and draw all forces (make a free-body diagram). Find the sum of both the horizontal and vertical force components. Find the net torque. All the sums are zero. Solve the system of equations.

ehild