exexcel M2 - rigid bodies - forces exeted on a pole by a wall

I am confused about which way to indicate horizontal and vertical forces. In the two questions in the attachment the solutions have forces in different directions that I can't decide why they are the way round they are (apart from the fact that numerically they have to be). But if I was doing the drawing before the arithmetic, how would I know which way to draw them?

Sorry, can get the file to attach and can't see how to delete this post.

I think I get what you're saying without the attachment.

Do you know the principle that if a system is in equilibrium, all forces must act through a common point?

If not, it doesn't matter which way you draw your forces. If you've drawn it the wrong way (say you had the vertical force acting upwards, but it actually acts downwards) you will get a negative answer for that force

Thanks, that'll sort me out. I I just draw on lines in the way I feel they should go - that would be OK then.

Can you answer me this other confusion I have please: Why is it the wall exerting a force on the pole and not the pole exerting a force on the wall? I would have thought that the wall is just sitting there and along comes a pole and it's that that changes things.

N3L


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What is N3L?

Newton's third law

Thanks, that'll sort me out. I I just draw on lines in the way I feel they should go - that would be OK then.

Can you answer me this other confusion I have please: Why is it the wall exerting a force on the pole and not the pole exerting a force on the wall? I would have thought that the wall is just sitting there and along comes a pole and it's that that changes things.

Common point of confusion
they both do!

in your diagram you are concerned with the rod, the ladder etc.

so you only mark forces acting on the object of interest and not on the outside system

typically for a ladder against a smooth wall and rough ground there should be 4 forces acting on the ladder

weight, friction towards the wall, normal away from the wall, normal upwards from the gound

Well, there you go. That's what I would have thought but when the question specifically asked " what is the force exerted by the wall on the pole" I was a bit thrown. I'll go back to those questions and redo them the way round I think.