Consider an automobile moving at v mph that skids d feet after its brakes lock. Calculate how far it would skid if it was moving at 2v and the brakes were locked.

Answer 1

v average =vi/2
d = (vi/2) t
0 = vi - a t so t = vi/a
d = (vi/2)(vi/a) = (1/2)vi^2/a

if initial speed = 2 vi, same a
x = (1/2)(2 vi)^2 /a
x = 4 d
four times as far