Final answer:
When you pass a freight truck with a bouncing trailer, it is more likely that the trailer is heavily loaded.
Step-by-step explanation:
When you pass a freight truck with a trailer on a highway and notice that its trailer is bouncing up and down slowly, it is more likely that the trailer is heavily loaded rather than nearly empty.
This is because a heavily loaded trailer will have greater mass, causing it to have a slower bounce frequency. On the other hand, a nearly empty trailer will have less mass and will bounce at a higher frequency.
Therefore, the slow bouncing motion indicates that the trailer is heavily loaded.