Final answer:
A proper adjusted head restraint provides maximum protection in a rear-end collision by minimizing the motion of the head and neck, which helps protect against injuries such as whiplash.
Step-by-step explanation:
A proper adjusted head restraint will provide the most protection if a vehicle is struck from the rear. In the event of such a collision, the head restraint helps to minimize the motion of the occupant's head and neck, protecting against whiplash and other neck injuries. This is supported by an understanding of impulse, which is the product of the net force on an object and the time over which the force acts. Vehicle safety features, such as seat belts, airbags, and padded dashboards, contribute to increasing the collision time and therefore reducing the forces experienced by the occupants during an impact. Additionally, the tendency of modern cars to crumple upon collision is an intentional design that increases the collision time and reduces the forces further, thereby increasing survivability and reducing injuries.