Final answer:
A trailer on a freight truck that bounces slowly on the highway is more likely heavily loaded due to the higher mass leading to greater inertia, which results in slower oscillations of the suspension.
Step-by-step explanation:
When observing a freight truck with a trailer on the highway, and noticing that its trailer is bouncing up and down slowly, it indicates that the trailer is more likely to be heavily loaded. A heavily loaded trailer has more mass, which means that it has greater inertia. This causes the suspension to compress more under the weight and makes it less susceptible to rapid oscillations or bounces. On the other hand, a nearly empty trailer would have less mass, allowing the suspension to react more quickly to bumps and dips in the road, leading to a faster and potentially more pronounced bouncing movement.