1. The problem statement, all variables and given/known data What average net force is required to bring a 1500kg car to rest from a speed of 27.8m/s within a distance of 55m? 2. Relevant equations v^2=vo^2+2ad vf-vo/(time elapsed) 3. The attempt at a solution I know I need to calculate the acceleration first, so immediately I thought of taking the distance and dividing it by the speed in order to get time, doing that I got 1.92s. Then when I put the velocity over that time to get the acceleration, I thought i would get the correct acceleration but no. I got -14.48 and the book says its -7. The book uses the formula v^2=vo^2+2ad Now, my question is: Why doesn't t work my way. Please don't tell me, it's much easier if you use the v^2 formula because I still won't understand since my question is why doesn't the way I thought work.