Final answer:
Head restraints are the modern energy-absorbing devices that protect against serious neck injuries in a rear-end collision.
Step-by-step explanation:
The modern energy-absorbing device that protects against serious neck injuries in a rear-end collision is the head restraints. Head restraints, also known as headrests, are designed to limit the movement of the head and neck during a collision, reducing the risk of whiplash or other neck injuries.
When a rear-end collision occurs, the head and neck of the occupants are subjected to a sudden and forceful backward movement. The head restraints help to prevent excessive backward movement by providing support to the head, neck, and upper body. They absorb some of the energy generated during the collision, distributing it over a larger area and increasing the collision time, thus reducing the force experienced by the occupants.
For example, if a vehicle without head restraints is rear-ended, the occupants' heads may be thrown backward, causing their necks to hyperextend. However, with properly adjusted head restraints, the chances of such injuries are significantly reduced.