VIDEO TRANSCRIPT

Here is a free body diagram for a box which is at rest on an incline and it is also the picture for a box which is sliding at constant velocity down the incline, you can’t tell which is happening based in this picture. All this picture says is that there is no acceleration because the friction force going up the ramp is equal to the X-component of gravity going down the ramp. In part c, it says what would the picture look like if the box were given a shove and was sliding up the ramp? And the picture would look like this. You would have kinetic friction opposing motion as it always does because the velocity is up the ramp and so the friction force would be down the ramp and that would be the picture in part c.