If a vehicle travels at 40 mph, how much longer will it take to stop compared to traveling at 20 mph?

When evaluating the relationship between speed and stopping distance, it’s important to understand the physics involved in braking. The stopping distance of a vehicle is influenced by the square of its speed. This means that if the speed of a vehicle doubles, the stopping distance increases by four times.

In this scenario, when a vehicle travels at 40 mph, the stopping distance is not just twice that of traveling at 20 mph; rather, it is four times greater. This is due to the fact that kinetic energy, which must be dissipated to bring the vehicle to a stop, increases with the square of the speed. Therefore, when moving from 20 mph to 40 mph, the kinetic energy—and consequently the stopping distance—will increase dramatically.

Thus, if a vehicle is traveling at 40 mph compared to 20 mph, it will take significantly longer to stop, specifically four times longer, which aligns with the concept laid out in the correct answer.