Chapter 4.2, Problem 21R

To determine

To find: a system can have kinetic energy and potential energy at the same time.

Explanation of Solution

Introduction: Kinetic energy is energy due to motion.Potential energy is energy that is stored due to the interactions between objects.

Consider a ball falling from a height at a certain speed.

The ball due to its motion has kinetic energy, which depends on its mass and speed. While, due to its height from the ground, it has gravitational potential energy, which decreases, as its distance from the ground decreases. Thus this ball-Earth system has both kinetic energy and potential energy at the same time.

Consider another system, a swing in motion.

Due to the motion of the swing, the system has kinetic energy and due to the height of the swing above the ground, it has gravitational potential energy. The potential energy varies as the height of the swing varies. In addition, the kinetic changes when swing is pushed or when it slowed down. Thus, this system too has both kinetic energy and potential energy at the same time.

Conclusion: A system can have kinetic energy and potential energy at the same time.