How to show that acceleration is constant?

1. We can create a free-body diagram to show, that all forces acting on a particle equal 0. When no force is acting on a particle or sum of forces equals 0, then acceleration is constant.
2. Knowing that acceleration is constant, we can plot a graph showing velocity versus time. If acceleration is constant, then our graph should form a straight line (because velocity will not change).

B) as the temperature increases, the kinetic energy of the particles increases.|-/