Lecture Notes on Kinetic Energy

Introduction to Kinetic Energy

• Definition: Kinetic energy is the energy stored in moving objects.
  • Example: A train, a Formula One car, and a roller coaster all have kinetic energy.
  • Note: Stationary objects, like a parked car, have no kinetic energy.

Calculating Kinetic Energy

• Equation:
  • Kinetic Energy (KE) in Joules = 0.5 × Mass (kg) × (Speed (m/s))²
  • Important: This equation is not provided in exams; it must be memorized.

Energy Conversion in Moving Objects

• Example: A car
  • Runs on petrol, a store of chemical energy.
  • Chemical reactions in the engine convert chemical energy into kinetic energy as the car moves.

Sample Calculation

1. Problem: Calculate KE for a car
   • Car mass: 700 kg
   • Car speed: 20 m/s
   • Solution:
     • KE = 0.5 × 700 kg × (20 m/s)² = 140,000 Joules
     • Conversion: 140,000 Joules to Kilojoules (kJ) = 140 kJ

Practice Question

• Problem: Calculate KE for a cyclist and bike
  • Total mass: 100 kg
  • Speed: 15 m/s
  • Solution:
    • KE = 0.5 × 100 kg × (15 m/s)² = 11,250 Joules
    • Conversion: 11,250 Joules to Kilojoules = 11.25 kJ

Calculating Mass from Kinetic Energy

• Problem: A tennis ball traveling at 50 m/s has a KE of 75 Joules. Find the mass.
  • Solution:
    • Rearrange KE formula to find mass:
      • Mass = KE / (0.5 × (Speed)²)
    • Calculate: Mass = 75 Joules / (0.5 × (50 m/s)²) = 0.06 kg

Conclusion

• By now, you should be able to:
  • Describe kinetic energy.
  • Calculate kinetic energy for a moving object.
• Additional Resources: Vision workbook for more practice questions.