Chapter 3, Problem 33A

Many automobile passengers suffer neck injuries when struck by cars from behind. How does Newton’s law of inertia apply here? How do headrests help to guard against this type of injury?

To determine

The application of Newton’s law of inertia in explaining neck injuries and role of headrest in guarding against this type of injury.

Explanation of Solution

Introduction:

As per Newton’s law of inertia, a body resists any change in its state of rest or motion.

When a car experiences a sudden jerk from behind due to collision with other car, the part of the body that is in direct contact with the car suffers a change in velocity due to the external force applied by the other car from behind. The neck is not in direct contact with the car, so it keeps moving with the same velocity as before the collision but the upper and lower part of the body move at different velocity, hence the neck experience a sudden jerk in backward direction resulting in injury.

The headrest helps in avoiding this type of injury by providing a support in contact with the neck and the car. So, the whole body of the passenger comes in contact with the car and moves with the car.

Conclusion:

Hence, Newton’s law of inertia explains the reason for neck injuries and headrest can be used to avoid this type of injury.