If you're in a car moving at a high speed, and you stop abruptly, what would

happen when wearing a seatbelt as opposed to not wearing a seat belt?

Which of Newton's 3 laws would apply?

A person would fly forward out of there seat and it's Newton's 1st law.

Explanation:

Newtons first law is an object will remain at rest or in uniform motion until an external force is applied.

So when someone is driving and there car stops suddenly, the person would keep moving forward