Question

Jane has a mass of 40 kg. She pushes on a 50 kg rock with a force of 100 N. What force does the rock exert on Jane?

Answer 1

I know something that a lot of people know but they get in trouble when they try to use it.  I got it a long time ago from my old school buddy Ike Newton.  I'll tell it to you, but you have to keep it to yourself, don't spread it around, and don't tell a lot of people where you got it.  

Here it is:

For every action, there is a reaction that is EQUAL and opposite.

That means that if Jane pushes on the rock with 100 Newtons of force,

then The rock pushes on Jane with 100 Newtons of force.

It doesn't matter how much Jane's mass is, it doesn't matter what the mass of the rock is, and it doesn't even matter whether Jane is moving, or the rock is moving, or both of them are moving.  If there's an action, then you can bet yer britches that there's a RE-action, and the RE-action is EQUAL and OPPOSITE to the action.

Why is this so hard ?