What is the coefficient of static friction between the ladderand the f

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Okay this one is really starting to get on my nerves. Drawing in the attachment.


Mass of ladder is 12kg. Mass of painter is 60kg. The ladder begins to slip when the person is 70percent up the ladder. The wall is frictionless.

What is the coefficient of static friction between the ladderand the floor?


I am unsure about where i should set the axis of torque, at the painter, the CM of the ladder or the wall?

 

[dextercioby]

Since the ladder would rotate,what is the center of rotation??

Daniel.

 

[NateTG]

Dex's answer is technically correct, but a bit misleading. You could pick anywhere that you like as the center of rotation because this is esentially a statics problem. Just make sure that you're calculating all of the torques about that point. Typically, people will chose a point that makes the calculation convenient like a location where many forces are applied - for example, the base of the ladder.

This problem can be rephrased as "what is the minimum coeficient of friction necessary to keep the ladder from slipping when the painter is 70% up the ladder?"