Final answer:
A trailer bouncing up and down slowly while passing a freight truck on a highway is more likely to be heavily loaded rather than nearly empty.
Step-by-step explanation:
When a trailer bounces up and down slowly while passing a freight truck on a highway, it is more likely that the trailer is heavily loaded rather than nearly empty. This is because a heavily loaded trailer has more mass, which causes it to have a lower natural frequency, resulting in slower and more pronounced bouncing.