Overview
This lecture explains kinetic energy, provides the formula to calculate it, demonstrates worked examples, and discusses how to rearrange the equation to solve for different variables.
What is Kinetic Energy?
- Kinetic energy is the energy stored in moving objects.
- Stationary objects have zero kinetic energy.
Kinetic Energy Formula
- The formula: Kinetic energy (J) = 0.5 × mass (kg) × speed (m/s)².
- The formula is not given in exams and must be memorized.
- Speed must be measured in meters per second (m/s).
Worked Examples
- Example 1: A 700 kg car moving at 20 m/s has kinetic energy of 140,000 J (or 140 kJ; 1 kJ = 1,000 J).
- Example 2: Cyclist and bike with mass 100 kg, speed 15 m/s: kinetic energy = 11,250 J (or 11.25 kJ).
- Example 3: A tennis ball traveling at 50 m/s with 75 J kinetic energy: mass = 0.06 kg (rearranged formula).
Rearranging the Formula
- To find mass: mass = kinetic energy ÷ (0.5 × speed²).
Key Terms & Definitions
- Kinetic energy — energy stored in a moving object.
- Joule (J) — unit of energy.
- Kilojoule (kJ) — 1,000 joules.
- Mass — amount of matter in an object, measured in kilograms (kg).
- Speed — how fast an object moves, measured in meters per second (m/s).
Action Items / Next Steps
- Memorize the kinetic energy formula.
- Practice calculations with different variables.
- Review additional kinetic energy questions in the revision workbook.