When I was in highschool, to get out of a speeding ticket, I was prepared to show that I could not have come to a full stop where the officer pulled me over if I was going as fast as he claimed (53mph), even with ideal assumptions (zero reaction time and perfect braking performance), which is quite an assumption for the 30 year-old car I was driving at the time. I never got a chance to test it in court, because the officer didn't show up on my court date.