Final answer:
A properly adjusted safety belt must fit snugly across the pelvis and chest, with the lap belt positioned low on the hips and the shoulder belt across the shoulder and chest, away from the neck and face. This positioning works effectively with airbags to minimize impact force in a collision.
Step-by-step explanation:
A properly adjusted safety belt should be worn tightly enough to keep it in place across the pelvis and chest, without any slack. The lap belt should sit low across the hips, not the stomach, and the shoulder belt should lie across the shoulder and chest without crossing the neck or face. Ensuring a correctly positioned safety belt is vital because it allows the airbags and other safety features of the vehicle to function most effectively in the event of a collision. Airbags deploy upon impact, in coordination with seat belts, to minimize serious injuries by allowing the net force on the occupants to act over a longer duration, thus reducing the resultant force of impact on the individual.