Overview
This lecture explains the concept of kinetic energy, provides the formula for calculating kinetic energy, and walks through example problems involving its calculation.
What is Kinetic Energy?
- Kinetic energy is the energy stored in moving objects.
- Stationary objects do not have kinetic energy.
The Kinetic Energy Equation
- the equation for kinetic energy: Kinetic Energy (J) = 0.5 × mass (kg) × speed (m/s)².
- The unit for kinetic energy is joules (J).
- The speed must be in meters per second (m/s).
- You must memorize the kinetic energy equation for exams, as it is not provided.
Example Calculations
- Example 1: A car with a mass of 700 kg and speed of 20 m/s has kinetic energy of 140,000 J (or 140 kJ after dividing by 1,000).
- Example 2: A cyclist and bike with a total mass of 100 kg at 15 m/s has kinetic energy of 11,250 J (or 11.25 kJ).
- To convert joules to kilojoules (kJ), divide by 1,000.
Rearranging the Equation
- To find mass when kinetic energy and speed are known: mass = kinetic energy ÷ (0.5 × speed²).
- Example: A tennis ball with kinetic energy 75 J and speed 50 m/s has a mass of 0.06 kg.
Key Terms & Definitions
- Kinetic Energy — Energy stored in moving objects.
- Joule (J) — The unit of energy.
- Kilojoule (kJ) — Equal to 1,000 joules.
Action Items / Next Steps
- Memorize the kinetic energy formula for exams.
- Practice more kinetic energy calculation problems from the revision workbook.