Final answer:
Tractors without trailers stop more quickly due to less mass compared to fully loaded tractor-trailers. A slowly bouncing trailer is indicative of a heavy load since the weight dampens the suspension system's movement.
Step-by-step explanation:
In terms of stopping distance, the accurate statement when comparing tractors without trailers to fully loaded tractor-trailers is that tractors without trailers stop more quickly. Heavily loaded tractor-trailers have a larger mass which results in a larger momentum when moving and therefore require a greater distance and time to stop. In contrast, a tractor without a trailer has less mass and can stop over a shorter distance.
Observing a freight truck with a trailer bouncing up and down slowly on the highway hints that it is more likely to be heavily loaded. A nearly empty trailer would bounce more rapidly due to less damping of the suspension system. Therefore, the slow bouncing indicates the presence of a heavy load that dampens the springs of the trailer, reducing the amplitude of the bounces and making them appear slower.