A man driving a car at 35 mph hits his brakes suddenly to avoid hitting a dog. Everything in the front seat of his car slides forward and into the floorboard. Which of
Newton's laws does this illustrate?

Inertia; Newton's First Law

Explanation:

When you hit you're breaks, the force you feel that pulls you forward is due to inertia.

Newton's first law says that "every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force." The question is a perfect example of this.

answer: the answer is a

conservation of mass

mass before something happens = mass afterwards