The sprinter accelerates on the running track. Draw a free-body diagram of the sprinter with the acting forces. Try as best you can to let the length of the vectors reflect the relative magnitudes of the forces.

We now assume that the sprinter is accelerated with a constant, horizontal driving force from the kick-off towards the ground, F = 400 N, all the way from the start to the finish line at 100 m. The mass of the sprinter is m = 80 kg.