Final answer:
A properly adjusted head restraint provides maximum protection when a vehicle is rear-ended, minimizing whiplash injuries by preventing extreme head movement. Safety features like airbags and seatbelts use the principle of impulse to increase the time over which a force acts, reducing the force on passengers.
Step-by-step explanation:
A properly adjusted head restraint will provide the most protection if a vehicle is struck from the rear. In such a scenario, the head restraint prevents excessive backward movement of the head relative to the torso, minimizing the risk of whiplash injuries during a collision. These safety features, including the airbags and seatbelts, are part of a car's passive safety system designed to protect passengers from the forces of a collision.
When a car is struck, especially from the rear, the occupants are subjected to rapid changes in momentum. The concept of impulse, which is the product of net force and the time over which it acts, is fundamental in understanding how safety features like airbags and padded dashboards help to reduce the severity of those forces on the occupants. By increasing the time over which a force acts, the overall force exerted on the occupants is reduced, thereby lowering the risk of injury.