Final answer:
To control speed when driving downhill due to gravity, you should shift to a lower gear or apply brakes to maintain a safe speed. This method helps manage the gravitational potential energy and prevent it from causing the vehicle to accelerate unsafely.
Step-by-step explanation:
When driving downhill, to control your speed due to gravity, you should Shift to a lower gear or apply brakes to slow to a safe speed. Truck brakes are used to control speed on a downhill run, where they convert the gravitational potential energy into increased internal energy (higher temperature) of the brake material. This conversion helps prevent the gravitational potential energy from turning into too much kinetic energy, which would increase the truck's speed dangerously. However, it's important to manage brake use since the mass of the truck is larger than the brake material, leading to a rapid temperature increase that might not dissipate quickly, risking brake failure.
Control of speed while descending is crucial for safety, as navigating a downhill route with too much velocity can result in loss of vehicle control. Therefore, the use of engine braking by shifting to a lower gear, which naturally limits the vehicle's speed by increasing engine resistance, is often recommended alongside careful brake application.