# Chapter 7: Energy

Kinetic energy (KE) is proportional to the square of the speed of the object; KE is therefore a number and **not **a vector. In order to understand how to use energy correctly, we will also need to discuss isolated systems, potential energy, and internal energy.

# Table of Contents

## Illustrations

- Illustration 7.1: Choice of System.
- Illustration 7.2: Representations of Energy.
- Illustration 7.3: Potential Energy Diagrams.
- Illustration 7.4: External Forces and Energy.
- Illustration 7.5: A Block on an Incline.

## Explorations

- Exploration 7.1: Push a Cart Around.
- Exploration 7.2: Choice of Zero for Potential Energy.
- Exploration 7.3: Elastic Collision.
- Exploration 7.4: A Ball Hits a Mass Attached to a Spring.
- Exploration 7.5: Drag the Ball to Determine PE(x).
- Exploration 7.6: Different Interactions.
- Exploration 7.7: Exploring Potential Energy Functions.

## Problems

- Problem 7.1: A ball slides in a frictionless bowl.
- Problem 7.2: A 12-kg box slides up a 26.56° frictionless ramp.
- Problem 7.3: A 12-kg box slides down a 26.56° frictionless ramp.
- Problem 7.4: A 12-kg box slides down a rough ramp.
- Problem 7.5: A mass is lifted by a string.
- Problem 7.6: A modified Atwood's machine.
- Problem 7.7: Three balls are thrown off the top of a building.
- Problem 7.8: A ball is dropped on a hard floor.
- Problem 7.9: An explosive collision.
- Problem 7.10: A spring gun.
- Problem 7.11: Collision between a mass and a mass connected to a spring.
- Problem 7.12: Collision between a mass and a mass connected to a spring.