How does kinetic energy affect the stopping distance of vehicle traveling at 30 mph compared to the same vehicle traveling at 60 mph

We have to determine the difference between the stopping distances of the vehicle traveling at 30 mph to the same vehicle traveling at 60 mph. Kinetic energy formula is: KE = 1/2 m v^2. - KE = - (Mi) m g d, where d stays for the stopping distance. Therefore: - 1/2 m v^2 = - (Mi) m g d. ( we can divide both sides by - m ); 1/2 v^2 = (Mi) g d; d = v^2 / 2 (Mi) g . The stopping distance is determined by the square of starting velocity and the effective coefficient of friction between the tires and the road ( Mi ). So d 1 = ( 30 ^2) / 2 (Mi) g = 450/ (mi) g; and: d 2 = ( 60^2 ) / 2 (Mi) g = 1800/ (Mi) g; d 1 : d 2 = 1/4; d 2 = 4 d 1. It affects that the second stopping distance becomes 4 times greater than the first.