1. The problem statement, all variables and given/known data Friction coefficient between an athlete's shoes and ground is 0.9 . Suppose Superman wears these shoes and runs a 50m race.There is no upper limit on his capacity of running at high speeds . Starting from rest, what will be the minimum time before he finishes the race ? 2. My views I am confused. I read that its the external force friction which allows acceleration to be possible. But friction also opposes relative motion. So in the above situation, is friction the force acting on accelerating Superman or is it retarding him ?