Sara is sitting in the back seat as her father drives at a constant speed.

If Sara's father presses on the brakes quickly slowing the car down, what slows Sara down?

A.

air resistance on the inside of the car

B.

air resistance on the outside of the car

C.

the seat pushing forward on her

D.

her seat belt pulling back on her

D.

her seat belt pulling back on her

Explanation:

The car, Sara, her father and the air inside the car are all moving at constant speed. When the car quickly slows down, Sarah, her father and the air try to continue with the constant motion they were undergoing before.

The air resistance from outside the car has no effect on slowing Sara down, and neither the air inside the car (which was moving at constant speed). The seat is not pushing forward on her, and in any case the friction between her and the seat could intervene, but never "pushing" on her.

The correct answer here is that the seat belt pulls her back slowing her constant speed motion.