In the last example of chapter $3$ b in module $3,$ the problem was about a block that being pulled by a variable tension where the variation of T vs time is given in a graph form. The net force in this case is also variable in time and its graph can be constructed since there are only two forces acting in the horizontal direction, the tension $T,$ and the friction force $f.$ The net force graph looks like the following:

Use the impulse$-$momentum theorem

$vec(G)=$vec$(G)(t_2)-$vec$(G)(t_1)={\displaystyle \underset{t_1}{\overset{t_2}{}}}{F}_{\text{N}\text{e}\text{t}}dt$

to find:

a$.$ The stopping time if we assume it will stop after $8$ seconds.

b$.$ The velocity of the block at $t=6s$