Assignment on friction

Homework Statement

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

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.

Homework Equations

I know that:
To be static, torque - F(r)sinthetha and that Torque(net) = 0
Coefficient of static friction = F(friction) / Normal

The Attempt at a Solution

I think I might need tosplit it into components and set Fnet(x) and Fnet(y) to 0.
I need to find N and Ffriction to find Uk...

For the second question, I don't know where to start. I was never good at estimation problems.

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Redbelly98
Staff Emeritus
Homework Helper

Welcome to Physics Forums.
goldentrinket;2954322 [h2 said:
Homework Equations[/h2]

I know that:
To be static, torque - F(r)sinthetha and that Torque(net) = 0
Coefficient of static friction = F(friction) / Normal

The Attempt at a Solution

I think I might need tosplit it into components and set Fnet(x) and Fnet(y) to 0.
I need to find N and Ffriction to find Uk...
After drawing a free body diagram, yes, you look at force components and set Fx,net=0 and Fy,net=0.

That gives you two equations. For a third equation, you set Torquenet=0 as well.

For the second question, I don't know where to start. I was never good at estimation problems.
I recommend starting a separate thread to ask this, since this is a separate, unrelated question. Start by drawing a free body diagram.