Final answer:
To check the 5th wheel jaws locking, pull the tractor gently forward. A trailer bouncing slowly on a highway is likely nearly empty, as a heavy load would offer more stability.
Step-by-step explanation:
To check that the 5th wheel jaws have locked behind the trailer's kingpin, the correct method is c) Pull the tractor gently forward. This action will confirm that the connection is secure and prevent the trailer from detaching while the vehicle is in motion. In this context, option a), inspecting the trailer lights, option b), kicking the tires, and option d), honking the horn twice are not the correct methods for checking the locking mechanism between the tractor and the trailer.
Regarding the second question, when you observe a freight truck's trailer bouncing up and down slowly on a highway, it is more likely that the trailer is nearly empty. A heavily loaded trailer usually has less bounce due to the weight providing more stability and less suspension movement. The observation of slow bouncing indicates that there is minimal weight in the trailer, allowing for more movement from the suspension.