If the net force is so as to push a particle of mass M in the direction in which it is already moving, you would expect the particle's speed to increase. If the net force has a constant magnitude F, then the particle will accelerate with an acceleration of magnitude a=F/M (from Newton's Second Law that F = ma ).

1.) Assume that the particle has initial speed u. Find its final kinetic energy K_f in terms of u, M, F, and D.