This isn't actually a homework question, it's for a vehicle safety project at work, but I think it fits in this forum. 1. The problem statement, all variables and given/known data A truck is traveling down the road at 60 mph, and begins to decelerate at a rate of 0.8 g. I'd like to find the total distance it takes the truck to stop, and come up with a formula for the velocity as a function of displacement from the original braking point. 2. Relevant equations I think that the relevant equation is v2 = 2a(s2-s1)+v12 3. The attempt at a solution Well, I know the truck is traveling at 88 fps, and slowing at a rate of 0.8 * 32fps2, so it will take 88 fps / (32.2 fps2 * 0.8 g) * 44 fps = 150 feet to stop But when I plug those numbers into the above equation, I get v2 = (2 * (0.8 * 32.2 * 60 / 88) * (-x) + (60)2)0.5 That has the right y-intercept (65 mph), but the wrong x-intercept, around 104' If I change the "2" on the right side of the equation to 1.38, it looks right, but I can't work out why it would be 1.38 instead of two. Argh! Any help much appreciated!