The stopping distance of a car is the number of feet that the car travels after the driver starts applying the brakes. The stopping distance of a certain car is directly proportional to the square of the speed of the car, in miles per hour, at the time the brakes are first applied. If the car’s stopping distance for an initial speed of miles per hour is feet, what is its stopping distance for an initial speed of miles per hour?
Lets read the question and highlight the critical words:
The stopping distance of a certain car is directlyproportional to the square of the speed.
That is – the distance equals a constant times the speed squared.
If we double the speed the distance of 17 feet would be quadrupled (2 square is 4) and will equal 68 feet.