2. Which of the following is an example of Newton's Third Law? A. A ball rolling downhill. B. A person pushing a wall, and the wall pushing back. C. A car speeding up. D. A leaf falling from a tree. thingy cannot be created or destroyed.

The correct answer is **B. A person pushing a wall, and the wall pushing back.**<br /><br />Here's why:<br /><br />Newton's Third Law states that for every action, there is an equal and opposite reaction. This means that whenever one object exerts a force on another object, the second object exerts an equal and opposite force back on the first object.<br /><br />* **A. A ball rolling downhill:** This demonstrates gravity and potentially friction, but not Newton's Third Law.<br />* **B. A person pushing a wall, and the wall pushing back:** The person exerts a force on the wall (action), and the wall exerts an equal and opposite force back on the person (reaction). This is a clear example of Newton's Third Law.<br />* **C. A car speeding up:** This demonstrates acceleration due to a force, but doesn't specifically illustrate the equal and opposite reaction aspect of Newton's Third Law.<br />* **D. A leaf falling from a tree:** This demonstrates gravity, but not Newton's Third Law.<br /><br />The statement "thingy cannot be created or destroyed" refers to the Law of Conservation of Mass (or in more modern physics, the Law of Conservation of Mass-Energy), which is a separate principle from Newton's Third Law.<br />