This acceleration is for any change in velocity. It doesn’t matter if the object is increasing or decreasing in speed—it’s still an acceleration. If you know the acceleration for something, you can find the stopping distance using the following kinematic equation ().
In this expression, v1 is the starting velocity (20 mph in this calculation) and v2 would be the final velocity—hopefully zero since it will stop. So, with a known acceleration the stopping distance (Δx) would be: