Question

A car company is testing seatbelts using crash test dummies. The company finds that when cars come to a sudden stop, the crash test dummies' bodies continue to move forward. The seat belt keeps the crash test dummies from hitting the back of the seat in front of them.

Why do the crash test dummies' bodies continue to move forward even though the car stopped?
A.
The friction opposing their bodies' movement keeps them in motion.
B.
The forward acceleration of the car keeps them in motion.
C.
The gravity pulling on the car keeps them in motion.
D.
The inertia of their bodies keeps them in motion.

Answer 1

D. The inertia of their bodies keeps them in motion.

Explanation: According to Newton's first law, an object in motion stays in motion unless acted on by a net external force. When the car stops suddenly, the dummies tend to keep moving forward due to their inertia. The seatbelt provides the external force that slows and stops them. Choices A, B, and C are incorrect: friction and gravity are not the primary reasons, and the car's forward acceleration does not keep the dummies moving when the car is decelerating.