00:01
Talk about this question a small box is held in place against a rough vertical wall so rough vertical mall means there is a friction so this is the vertical wall and uh uh this is the box and the force is directed upward 28 degrees above the horizontal so this is how the force is acting which is 28 degrees above the horizontal the coefficient of the kinetic and the static friction between the box and the wall is 0 .4 and 0 .3.
00:31
The box slides down unless the applied force has a magnitude of 23 newton.
00:36
So if this is 23 newton, the blocks doesn't slide down.
00:39
What is the mass of the box? so it will, let's draw the fbd.
00:45
It will have a reaction force over here.
00:47
It will have a friction force above because it has a tendency to slide down.
00:52
And this is the weight of the of the box.
00:59
Now, we are going to make the components of this 23 newtons.
01:03
That's going to be a 23 cost 28 and 23 sine 28.
01:11
So since this is at rest, we are going to say that r is equal to 23 cost 28 degrees.
01:19
That's called equation 1.
01:21
And we are going to say that 23 sine 28 plus friction force is equal to weight.
01:29
The friction force is going to be mu times normal reaction...