Help with Torque | Troubleshooting Ladder Angles & Forces

[gibson72]

Ive been coming acrosse problems in this subject that I am not sure how to do.

for example

1.An 8.0m, 200-N uniform ladder rests against a smooth wall. The coefficient of static friction is 0.60 and the ladder makes a 50 degree angle with the ground. how far up the can an 800-N person climb before the ladder begins to slip?

for this problem I drew a free body diagram and I new were to place the different forces on it. I just do not know how to handle the information given to me as well as properly utilize it.

Also I understand how to do problems were sum of torque is in equilibrium such as a hanging sign or a lamp. I am having problems in general with problems that involve ladders at an angle against a wall with different forces, such as a person, on them.

 

[physics girl phd]

I'm glad you are doing well with the equilibrium problems!

Can you attach your free body diagram of this problem so we can see it?
I really want to check to see that you are putting in certain forces (like the friction), and how you've put in the person (who can move). Then we can better discuss where to go with this next.

 

[civil_dude]

Always sum moments about the point where the most unknown forces are. This is key. For this, I would sum the moments about the bottom of the ladder. That way, your only unknown is the normal force of the wall on the upper part of the ladder. Then you now know a critical value. You also know that the friction force is independent of the angle or distance of the load. Ta Daaaa. Plug and chug from here.

If I have to solve it for you then it is $150/hr.

This is easy. Draw a good picture.