A marathon runner continues to run several meters beyond the finish line. This is an example of what the law of motion

Newton's first law of motion

Explanation:

Newton first law of motion states that a body will continue to be at rest on in a state of uniform motion unless an external force acts on it.

This is also known as the law of inertia.

What this law is trying to explain is that the runner won't be able to stop unless an external force acts on him to stop him from run. For example, a car moving in a straight direction will continue to do so at a constant speed unless an external force is exerted upon it maybe when the car hits an obstacle or brakes is applied it to. Or when a stone is at a position of rest, it won't move unless a force is exerted on it to cause to move.