A runner whose mass is 55 kg accelerates from a stop to a speed of 8 m/s in 3 seconds. (A good sprinter can run 100 meters in about 10 seconds, with an average speed of 10 m/s.)
What is the average horizontal component of the force that the ground exerts on the runner's shoes?
How much work is done on the point-particle system by this force? (Hint: use a fundamental principle, as applied to the point-particle system.)