### this is another exercise of the kind i just posted. it is interesting for me because the use of this formula is advised. i do not understand it and the formula is not explained.

The stopping distance d of a car after the brakes are applied varies directly as the square of the speed r, if a car traveling 40 mph can stop in 70 ft, how many feet will it take the same car to stop when its traveling 80 mph.use the following formula

d = kr^2

and you can get

**from the given information.**

*k*thanks in advance for any explanation or help of any kind.

eddy