Difficult Ladder Against Wall Torque Problem

[whoopie88]

Difficult Ladder Against Wall Torque Problem!

Homework Statement

An 85 kg person stands on a uniform 6.6 kg ladder that is 3.9 m long, as shown. The floor is rough; hence it exerts both a normal force, f1, and a frictional force, f2, on the ladder. The wall, on the other hand, is frictionless; it exerts only a normal force, f3. Using the dimensions in the figure, find the magnitudes of f1, f2, and f3.

Homework Equations

All forces and torque formulas.

The Attempt at a Solution

I found f1 - 898.6 N. I can't find f2 and f3, which I think are supposed to be equal. No matter what I try, I can't seem to get an answer. Here's my work:

Help please? Thanks in advance.

 

[Undoubtedly0]

Have you tried applying f = μN, where f is the frictional force and N is the normal force? Where you given the coefficient of friction, μ?

 

[whoopie88]

No; I wasn't given the coefficient of friction. My instructor, for all of our problems relating to torque, has made it clear that we do not need to apply f = μN.

 

[Undoubtedly0]

Alright. At the end of your work it looks like you wrote "f3 = 698.1N". Is this not what you were looking for?

 

[whoopie88]

That is what I was looking for, but that's an incorrect answer.

 

[Undoubtedly0]

Got it. Just one last question; how far up (or down) the ladder does the problem say the man is standing?

 

[whoopie88]

That information is not given.

Here is the diagram that goes along with the problem:

 

[Undoubtedly0]

Great. It is hard to see your work in the picture, but try solving for the torque around the top of the ladder. Show me the equation you set up. I got to a different answer.

 

[SammyS]

Find the torque (moment) about the contact point at the bottom of the ladder. It doesn't involve f₁ or f₂ and it doesn't depend
upon the person's distance up the ladder.