Key Takeaways for GCSE Energy Revision

1. Energy Stores and Transfers

  • 8 Energy Stores:
    1. Kinetic (moving objects, e.g., a speeding car).
    2. Gravitational Potential (height, e.g., a raised weight).
    3. Chemical (fuels/food, e.g., a battery).
    4. Elastic Potential (stretched/compressed objects, e.g., a spring).
    5. Thermal/Internal (heat, e.g., boiling water).
    6. Magnetic (interacting magnets, e.g., repelling poles).
    7. Electrostatic (charged objects, e.g., a balloon rubbed on hair).
    8. Nuclear (atomic nuclei, e.g., uranium in reactors).
  • Energy Transfers:
    • Mechanical work (force × distance, e.g., lifting a box).
    • Heating (conduction/convection, e.g., a hot cup cooling).
    • Radiation (light/sound, e.g., sunlight warming the Earth).
    • Electrical work (current in a circuit, e.g., a lamp lighting).
  • Conservation of Energy:Energy cannot be created or destroyed, only transferred between stores.
    • Example: A ball thrown upwards converts kinetic → gravitational potential → kinetic energy.

2. Energy Calculations

Key Equations:

  • Kinetic Energy:
    Ek=12mv2Ek​=21​mv2
    Example: A bullet (mass 0.015 kg, speed 240 m/s):
    Ek=12×0.015×2402=432 JEk​=21​×0.015×2402=432J
  • Gravitational Potential Energy:
    Ep=mghEp​=mgh
    Example: A 50 kg boy climbing 440 m (Taipei 101):
    Ep=50×9.8×440=215,600 JEp​=50×9.8×440=215,600J
  • Elastic Potential Energy:
    Ee=12ke2Ee​=21​ke2
    Example: Spring (k = 2000 N/m, compressed 0.08 m):
    Ee=12×2000×0.082=6.4 JEe​=21​×2000×0.082=6.4J

Tip: Always convert units to kg, m, s before calculations!

3. Work and Power

  • Work Done:
    W=F×sW=F×s
    Example: Braking a car (force = 5000 N, distance = 60 m):
    W=5000×60=300,000 JW=5000×60=300,000J
  • Power:
    P=Energy TransferredTimeorP=WtP=TimeEnergy Transferred​orP=tW​
    Example: Lifting 140 kg to 1.2 m in 0.6 s:
    P=140×9.8×1.20.6=2700 WP=0.6140×9.8×1.2​=2700W

Trick: For stairs, use vertical height, not slope length!

4. Specific Heat Capacity

  • Equation:
    ΔE=mcΔθΔE=mcΔθ
    Example: Heating 0.3 kg milk (c = 3800 J/kg°C) by 66°C:
    ΔE=0.3×3800×66=75,240 JΔE=0.3×3800×66=75,240J

Practical Tips:

  • Use insulation to reduce energy loss.
  • Measure temperature immediately after heating to minimise errors.

5. Efficiency

  • Equation:
    Efficiency=Useful Output EnergyTotal Input Energy×100%Efficiency=Total Input EnergyUseful Output Energy​×100%
    Example: Steam engine (18 kJ useful out of 150 kJ input):
    Efficiency=18150×100%=12%Efficiency=15018​×100%=12%

Improving Efficiency:

  • Reduce friction (lubrication, wheels).
  • Reduce air resistance (streamlining).

6. Energy Resources

  • Non-Renewable:
    • Finite supply (coal, oil, gas, nuclear).
    • Disadvantages: CO₂ emissions, acid rain (coal).
  • Renewable:
    • Infinite supply (solar, wind, hydroelectric, tidal).
    • Example: Tidal barrage (Severn Estuary) uses gravitational potential energy of water.

Power Stations:

  • Coal: 20% UK electricity (high CO₂).
  • Wind: 11% UK electricity (unreliable but clean).

7. Exam Tips & Common Mistakes

  • Units: Check kg → g (÷1000), cm → m (÷100).
  • Energy Transfers: Light/sound are transfers, not stores!
  • Graphs: Use bar charts for categoric variables (e.g., fuel types).

Trick: For conservation problems, equate initial and final energy (e.g., kinetic → gravitational potential).

8. Required Practicals

  1. Specific Heat Capacity:
    • Measure energy transferred electrically (E = VIt).
    • Calculate c=EmΔθc=mΔθE​.
  2. Thermal Insulation:
    • Test materials by measuring temperature drop over time.
    • Best insulators = least temperature change (e.g., bubble wrap).

Final Tip: Practice past papers to spot patterns in questions!
Example Question:
A meteor (mass 0.05 kg, speed 30 km/s) has kinetic energy:
Ek=12×0.05×(30, ⁣000)2=22, ⁣500, ⁣000 JEk​=21​×0.05×(30,000)2=22,500,000J
(Convert km/s → m/s first!)

Questions

  1. State three examples of how you use energy every day.
  2. Give an example of a fossil fuel.
  3. Why are metals good thermal conductors?
  4. Describe the energy stored in a moving bicycle.
  5. Explain why the statement “A car battery stores electrical energy” is incorrect.
  6. A ball is thrown upwards. Describe the energy transfers from the moment it leaves the hand until it is caught again.
  7. Calculate the kinetic energy of a bullet of mass 0.015 kg travelling at 240 m/s.
  8. A boy of mass 50 kg climbs the Taipei 101 Tower (440 m). Calculate his increase in gravitational potential energy.
  9. A car accelerates from 15 m/s to 20 m/s. Its mass is 1500 kg. Calculate the increase in kinetic energy.
  10. A spring (spring constant 2000 N/m) is compressed by 8 cm. Calculate its elastic potential energy.
  11. A meteor (mass 0.05 kg) travels at 30 km/s. Calculate its kinetic energy.
  12. A ball (mass 100 g) is thrown vertically upwards at 15 m/s. Calculate its maximum height.
  13. A stretched bow stores 64 J of elastic potential energy. It fires a 20 g arrow. Calculate the arrow’s speed.
  14. A car rolls down a 1 in 5 slope. After travelling 20 m, calculate its speed. (Mass = 1200 kg)
  15. Define work done and state its unit.
  16. A crane lifts a 12,000 N weight through 30 m in 90 s. Calculate its power output in kW.
  17. Two students run upstairs. Peter (760 N) takes 3.8 s, and Hannah (608 N) takes 3.04 s. Who is more powerful?
  18. Define specific heat capacity and state its units.
  19. Calculate the energy needed to warm 60 kg of concrete from 15°C to 45°C. (Specific heat capacity = 800 J/kg°C)
  20. A 200 W heater warms concrete. How long does it take to supply the energy calculated in Q19?
  21. Milk (0.3 kg) is heated in a microwave (700 W) for 1 minute. Calculate its temperature rise. (Specific heat capacity = 3800 J/kg°C)
  22. Explain how loft insulation reduces energy dissipation.
  23. Define efficiency and write its equation.
  24. A steam engine uses 150 kJ of coal energy and does 18 kJ of useful work. Calculate its efficiency.
  25. A motor lifts an 80 kg crate 3 m in 12 s with 800 W input. Calculate its efficiency.
  26. State two advantages and two disadvantages of wind power.
  27. Why is nuclear power considered non-renewable despite having long-lasting fuel?
  28. Calculate the gravitational potential energy of a suitcase (18 kg) placed 2.5 m above a train floor.
  29. A gymnast (55 kg) lands on a trampoline from 5 m. The trampoline’s spring constant is 35,000 N/m. Calculate its compression distance.
  30. Lead shot (50 g) falls 1 m in a tube 50 times. Calculate the total decrease in gravitational potential energy.
  31. The specific heat capacity of lead is 160 J/kg°C. Calculate the temperature rise of the lead shot in Q30.
  32. Explain why the actual temperature rise in Q31 might be less than calculated.
  33. A girl kicks a football (450 g) with 300 N force over 0.2 m. Calculate the ball’s speed.
  34. Define renewable and non-renewable energy resources. Give one example of each.
  35. State two environmental problems caused by burning coal.
  36. A tidal barrage generates electricity. Explain why it is more reliable than wind power.
  37. A pumped storage power station pumps water uphill during low demand. Explain its usefulness.
  38. A wind turbine produces 4 MW maximum power but only operates at 10% capacity. How many turbines replace a 2000 MW coal plant?
  39. A car (1500 kg) travels at 15 m/s. Calculate its kinetic energy.
  40. The same car accelerates to 25 m/s. Calculate the increase in kinetic energy.
  41. A pirate boat ride swings a child (60 kg) with a kinetic energy increase of 10,830 J. Calculate her speed.
  42. Sketch a graph showing gravitational potential energy changes during the pirate boat swing.
  43. A winch lifts a truck (2000 N) 15 m. Calculate the work done.
  44. The winch operates at 6 kW and moves at 5 m/s. Calculate the time taken to lift the truck.
  45. Calculate the efficiency of the winch if it uses 180,000 J of energy to lift the truck.
  46. A Severn Barrage tidal system has water flowing at 50,000 kg/s from 200 m height. Calculate the gravitational potential energy transferred per second.
  47. If the barrage generators are 80% efficient, calculate their power output.
  48. Explain why biofuels are considered carbon neutral.
  49. A student measures the specific heat capacity of water. Describe the experiment and necessary calculations.
  50. Explain the difference between random and systematic errors in an experiment.

Answers

  1. Examples: Using electrical appliances, heating food, transportation.
  2. Example: Coal, oil, or natural gas.
  3. Metals have free electrons that transfer energy quickly through collisions.
  4. Kinetic energy store.
  5. Batteries store chemical energy, not electrical energy. Electrical energy is transferred when the battery is used.
  6. Kinetic → Gravitational potential → Kinetic (energy dissipated as thermal/sound).
  7. Ek=12mv2=12×0.015×2402=432 JEk​=21​mv2=21​×0.015×2402=432J.
  8. Ep=mgh=50×9.8×440=215,600 JEp​=mgh=50×9.8×440=215,600J.
  9. ΔEk=12×1500×(202−152)=131,250 JΔEk​=21​×1500×(202−152)=131,250J.
  10. Ee=12ke2=12×2000×(0.08)2=6.4 JEe​=21​ke2=21​×2000×(0.08)2=6.4J.
  11. Convert 30 km/s to m/s: 30,000 m/s. Ek=12×0.05×(30,000)2=22,500,000 JEk​=21​×0.05×(30,000)2=22,500,000J.
  12. 12mv2=mgh⇒h=v22g=1522×9.8=11.5 m21​mv2=mgh⇒h=2gv2​=2×9.8152​=11.5m.
  13. 12mv2=64⇒v=2×640.02=80 m/s21​mv2=64⇒v=0.022×64​​=80m/s.
  14. Height drop: 205=4 m520​=4m. mgh=12mv2⇒v=2gh=2×9.8×4=8.9 m/smgh=21​mv2⇒v=2gh​=2×9.8×4​=8.9m/s.
  15. Work done = force × distance in direction of force. Unit: joule (J).
  16. P=Wt=12,000×3090=4000 W=4 kWP=tW​=9012,000×30​=4000W=4kW.
  17. Peter: P=760×4.53.8=900 WP=3.8760×4.5​=900W. Hannah: P=608×4.53.04=900 WP=3.04608×4.5​=900W. Equal power.
  18. Energy required to raise 1 kg of a substance by 1°C. Units: J/kg°C.
  19. ΔE=mcΔθ=60×800×30=1,440,000 JΔE=mcΔθ=60×800×30=1,440,000J.
  20. t=EP=1,440,000200=7200 s=2 hourst=PE​=2001,440,000​=7200s=2hours.
  21. Energy supplied: 700×60=42,000 J700×60=42,000J. Δθ=Emc=42,0000.3×3800=36.8°CΔθ=mcE​=0.3×380042,000​=36.8°C.
  22. Loft insulation traps air, reducing conduction and convection.
  23. Efficiency = (useful output energy / total input energy) × 100%.
  24. Efficiency = 18150×100=12%15018​×100=12%.
  25. Useful energy: mgh=80×9.8×3=2352 Jmgh=80×9.8×3=2352J. Efficiency = 2352800×12×100=24.5%800×122352​×100=24.5%.
  26. Advantages: Renewable, no emissions. Disadvantages: Unreliable, visual pollution.
  27. Uranium/plutonium are finite; they take millions of years to form.
  28. Ep=18×9.8×2.5=441 JEp​=18×9.8×2.5=441J.
  29. mgh=12kx2⇒x=2mghk=2×55×9.8×535,000=0.38 mmgh=21​kx2⇒x=k2mgh​​=35,0002×55×9.8×5​​=0.38m.
  30. Total GPE loss: 50×0.05×9.8×1=24.5 J50×0.05×9.8×1=24.5J.
  31. Δθ=Emc=24.50.05×160=3.06°CΔθ=mcE​=0.05×16024.5​=3.06°C.
  32. Energy is dissipated as sound/thermal energy in surroundings.
  33. Work done = force × distance = 300 × 0.2 = 60 J. Speed: v=2Ekm=2×600.45=16.3 m/sv=m2Ek​​​=0.452×60​​=16.3m/s.
  34. Renewable: Solar (replenished). Non-renewable: Coal (finite).
  35. CO₂ emissions (global warming), sulfur dioxide (acid rain).
  36. Tides are predictable; wind speed varies.
  37. Stores excess energy during low demand for use during peak times.
  38. Turbines needed: 20004×0.1=5004×0.12000​=500.
  39. Ek=12×1500×152=168,750 JEk​=21​×1500×152=168,750J.
  40. ΔEk=12×1500×(252−152)=300,000 JΔEk​=21​×1500×(252−152)=300,000J.
  41. v=2Ekm=2×10,83060=19 m/sv=m2Ek​​​=602×10,830​​=19m/s.
  42. Graph: PE decreases from A to B (lowest point), then increases to C.
  43. Work done = force × distance = 2000 × 15 = 30,000 J.
  44. Time = distance / speed = 15 / 5 = 3 s.
  45. Efficiency = 30,000180,000×100=16.7%180,00030,000​×100=16.7%.
  46. Ep=mgh=50,000×9.8×200=98,000,000 J/s=98 MWEp​=mgh=50,000×9.8×200=98,000,000J/s=98MW.
  47. Power output = 98 MW × 0.8 = 78.4 MW.
  48. CO₂ absorbed during plant growth equals CO₂ released when burned.
  49. Heat water with immersion heater, measure mass, temp change, and energy input. Use c=EmΔθc=mΔθE​.
  50. Random errors cause scatter (e.g., timing). Systematic errors shift all measurements (e.g., faulty instrument).