00:01
We begin this question by drawing the force that are acting on our system.
00:05
So the gravitational force acts on the crate.
00:09
Then there is a force that the floor exerts on the crate acting on that crate.
00:16
At the same time the gravitational force acts on the person.
00:22
And then the crate exerts some force on that person.
00:28
So these are the forces that are acting on our problem.
00:32
Then, to solve the problem, we have to apply newton's second law.
00:37
So first, let's apply the newton's second law to the crate.
00:41
So, the net force acting on the crate is equal to the mass of the crate times declaration of the crate.
00:49
Note that the crate is standing still, so it's not moving.
00:53
Therefore, declaration is equal to zero.
00:56
Let me choose my referential as being that everything that is pointing up is positive and everything that is pointing down is negative.
01:02
In this setup, the net force acting on the crate is equal to minus the weight of the crate plus the force that the floor exerts on the crate minus the force that the person exerts on the crate, which is equal to the weight force of this person, so minus the weight of the person...