Final answer:
Drivers should check wheels, tires, lights, brakes, hubs, trailer coupling, and cargo periodically for safe vehicle operation. Trailers that bounce up and down slowly are likely to be nearly empty, as heavy loads would dampen such movement.
Step-by-step explanation:
During a trip, a driver should check periodically several items related to the vehicle to ensure safety and prevent future accidents. These items include: For the specific information provided: knowing the distance a driver covers before hitting the brakes, how long it takes the truck to stop after hitting the brakes, and the total distance the truck covers to stop, are all essential for assessing vehicle performance and brakes' condition.
Regarding the observation question about the trailer bouncing up and down slowly, it is more likely that the trailer is nearly empty. A heavily loaded trailer would have less bounce due to the weight stabilizing the movement. Conversely, an empty trailer has less weight to dampen any movement, hence the noticeable bounce.