00:01
This problem is about friction.
00:03
In part a, you have to identify which force is making the block accelerate.
00:10
Well, when the block accelerates, the only object that can exert a force on it is the ground by either a normal force or a friction force.
00:20
And the friction force is the only one that acts horizontally.
00:23
So it has to be the friction force when makes the block accelerate.
00:35
Now in part b, we have to calculate the maximum acceleration and we have to understand that both the truck and the block are going to have the same acceleration because they are part of the same system.
00:51
So let's draw a free body diagram for the block.
00:57
We know that the block is accelerating to this side with a force friction, but that force of friction behaves in a particular way.
01:09
That force of friction matches any force that is exerted until a maximum point.
01:19
And then it falls back down and exerts a constant force...