Final answer:
The stopping distance of a car traveling at 120 km/h is 40 m.
Step-by-step explanation:
To find the stopping distance of a car traveling at 120 km/h, we can use the fact that the maximum braking force is approximately independent of speed. From the given information, we know that when the car is traveling 60 km/h, it can brake to a stop within a distance of 20 m. This means that the car's stopping distance is directly proportional to its initial speed. If the car is going twice as fast, 120 km/h, its stopping distance will also be twice as long. Therefore, the stopping distance of the car traveling at 120 km/h is 2 x 20 m = 40 m.