What was significant about the atomic theory that democrituis proposed?

An object moves from position +34m to the position -15m in 15 seconds. what is the total displacement? what is the total velocity?

Why is the energy that results from a roller coaster's position at the top of a hill referred to as potential energy?

If two students are running down the hall toward each other, trying to get to class, and they have the same mass and acceleration, what will happen when they collide? will their forces cancel out or will each one experience a reaction?