gistfile1.txt

formula 1: 

force = energy / distance
-> 
distance = energy / force


formula 2:

kinetic energy = .5 * mass * velocity^2
->
distance = .5 * mass * velocity^2 / braking force

formula 3:

braking force = friction * weight = friction * mass * 9.8

combining all formulas together we get:

distance = .5 * mass * velocity^2 / (friction * mass * 9.8)

distance = .5 * velocity^2 / friction / 9.8

distance = velocity^2 / friction / 4.9