A driver traveling at 25 mph in a school zone can brake to an emergency stop in 8 ft. Under similar conditions, what would be the braking distance if the car were traveling at 40 mph?

Answer 1

The braking distance is proportional to the kinetic energy, which means it is proportional to the square of the velocity.

So, multiply 8 ft by (40/25)^2.
You should get about 20.5 ft.

There will be an additional distance travelled while the driver responds to the emergency and applies the brake. That distance is proportional to speed, but they probably expect you to ignore it.