Final answer:
When going down a steep hill, a driver should shift to a lower gear for engine braking, which assists in controlling the vehicle's speed and prevents brake overheating.
Step-by-step explanation:
When driving down a steep hill, it's recommended to use a lower gear, which is sometimes called engine braking. By shifting to a lower gear, you allow the engine to help in slowing the vehicle down, which is essential for maintaining control and preventing the brakes from overheating and potentially failing. This practice relies on the physics of energy transformation and is relevant in situations such as the given scenario where a car coasts down a hill and eventually stops at a gas station.
It is also important to note that the steeper the hill and the heavier the vehicle, like a truck going down a 150 m high hill, the more essential it is to use engine braking to control speed. Moreover, the effectiveness of this method is influenced by factors like the angle of the hill's slope and the coefficient of static friction between the tires and the road surface.