Final answer:
The head restraint should be behind the middle of the person's head to provide support and prevent whiplash injuries during a rear-end collision.
Step-by-step explanation:
The correct answer is option True. When the head restraint is adjusted properly, it should be behind the middle of a person's head. The purpose of the head restraint is to prevent whiplash injuries during a rear-end collision. If the head restraint is positioned correctly, it can help support the head and neck, reducing the risk of injury.
The reason the head restraint needs to be behind the middle of the person's head is related to the center of mass. The center of mass of the head lies in front of its major point of support, which is the neck vertebrae.
This requires muscle action to hold the head erect, as shown in Figure 9.39. By adjusting the head restraint behind the middle of the head, it provides additional support and aligns the head with its center of mass, reducing strain on the neck and minimizing the risk of injury.
Therefore, it is important to adjust the head restraint properly to ensure its effectiveness in protecting against whiplash injuries.
The correct answer is False. When a head restraint is adjusted properly, it should be positioned at the level of the top of the ears and as close to the back of the head as possible.
This positioning helps to support the head in the event of a collision and can prevent or lessen the severity of neck injuries such as whiplash. Therefore, while the middle of the head is not the correct reference point, proper alignment is crucial for safety.
Regarding the balance of loads on the head, the center of mass of a load must be directly above a person's neck vertebrae for efficient carrying.
This is because the neck vertebrae provide the main support for the head and any additional weight on it.
Balancing the load directly above the support helps to maintain stability and minimize the effort required to carry the load, as it requires minimal muscle action to keep it erect rather than exerting additional force to counteract a load that is off-center.