Final answer:
To control speed when driving down a long steep hill, you should shift into a lower gear to make use of the engine's braking force instead of relying solely on the brakes, which is essential for vehicle safety.
Step-by-step explanation:
When driving down a long steep hill, you should shift into a lower gear to control your speed. Doing this uses the engine's braking force to help maintain a safe speed, reducing the need to apply the brakes continuously, which can lead to brake overheating and failure. It is similar to how cruise control maintains a car's speed, but in this case, it's the driver actively managing the vehicle's momentum. While cruise control is great for maintaining a set speed under normal driving conditions, it isn't advantageous on steep descents. Shifting to a lower gear is a better practice, combining the physics of friction, gravitational potential energy, and kinetic energy to safely navigate downhill roads.
Imagine a car, analogous to a situation where a truck is parked on a hill and then lets it run freely downhill. In both scenarios, the vehicle gains speed due to gravitational pull. If on a banked curve, the curve itself assists in managing the vehicle's speed without relying on friction alone. However, on a straight descent, shifting to a lower gear is crucial for speed control—allowing the engine to act as a complement to the conventional braking system by resisting the drive train's motion through engine compression.