A runner whose mass is 53 kg accelerates from a stop to a speed of 7 mfs in 4 seconds. (A good sprinter can run 100 meters in about 10 seconds, with an average speed of 10 mls.) (a) What is the average horizontal component of the force that the ground exerts on the runner's shoes? Average force = S N (b) How much displacement is there of the force that acts on the sole of the runner's shoes, assuming that there is no slipping? Displacement : E m (c) Therefore, how much work is done on the extended system (the runner) by the force you calculated in part (b)? work::1 (d) How much work is done on the point-particle system by this force? (Hint: use a fundamental principle, as applied to the pointparticle system.) we