practice problem notes

For 1a. The friction force is 20 N** and is opposing the motion. So the net force in the first time frame is 35-20=15 N.  Ultimately, via our kinematic equations, that leads to v= 6 m/s at t=2 s...
Also, one can use the area under the velocity curved to obtain the distance travelled. (That is, the position of the block.) As an example of this, to find the distance travelled between t=0 and t=2 s, you can use the area under the v(t) curve, which is, A=(6 m/s * 2 s)/2 = 6m. This method becomes particularly useful when the velocity curve gets complicated due to changes in acceleration. It is good to know how to calculate the area of rectangles, triangles (and a triangle on top of a rectangle).

**you don't need to know about mu for our exam tomorrow. You will be given friction forces in newtons.