Friction coefficient?

The friction coefficient between an athelete's ahoes and the ground is 0.90 . Suppose a superman wears these shoes and races for 50 m. There is no upper limit on his capacity of running at high speeds . What will be the minimum time that he will have to take in completing the 50 m starting from rest ?

Friction coefficient?
Start with the formula, F = ma. The force, F, he is able to exert is equal to his weight times the coefficient of friction. And his weight is his mass times the acceleration of gravity. So, F = 0.9mg, and 0.9mg = ma. Mass is on both sides, so it cancels. 0.9g = a, 0.9*9.81 m/s^2 = 8.83 m/s^2. His final velocity, Vf = SQRT(Vi^2 + 2ad), where Vi is his initial velocity (zero), a is his acceleration, and d is the distance he travels. So, Vf = SQRT(2*8.83*50) = 29.71 m/s. Because his acceleration is constant, his average velocity is 29.71/2 = 14.86 m/s. The time he takes is then d/Vave = 50/14.86 = 3.365 s.
Reply:the fundamental question: will spiderman race too?... :)


seriously, I think that we need also value of acceleration or another values...



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