Final answer:
Large trucks are most likely to lose speed when going up long steep hills due to the force of gravity acting against the truck's engine, making it difficult to maintain speed and posing a potential hazard.
Step-by-step explanation:
Large trucks are most likely to lose speed and cause a hazard when going up long steep hills. When a truck ascends a steep incline, the force of gravity works against the engine's ability to move the truck's large mass uphill. This can lead to a reduction in speed, potentially becoming a hazard to other drivers if the truck is unable to maintain a consistent speed with traffic or if other drivers aren't expecting the speed reduction. Trucks have to work harder to overcome gravitational forces pulling them back down the hill, and it can be challenging for the truck to maintain its speed. Comparatively, when going down long, gradual hills, truck brakes are often used to control the speed to prevent the conversion of gravitational potential energy into excessive kinetic energy, which could lead to the truck speeding up uncontrollably. The ideal speed on curves and acceleration lanes is generally maintained as long as the vehicle is functioning properly and the conditions permit.