A petrol-powered go-kart travels along a flat track at constant speed. Of the 50 000 J of chemical energy released by the fuel, 12 500 J is transferred as useful kinetic energy to the go-kart. Describe the useful energy transfer and the waste energy transfers that occur, and explain what is meant by the efficiency of this system.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A petrol-powered go-kart travels along a flat track at constant speed. Of the 50 000 J of chemical energy released by the fuel, 12 500 J is transferred as useful kinetic energy to the go-kart.
Model answer (4 marks)
Chemical energy in the fuel is the input energy store. The useful energy transfer is the 12 500 J that becomes kinetic energy of the go‑kart. The waste energy transfers are the thermal/heat energy produced by friction and engine heating and the sound energy emitted. Efficiency is the ratio of useful energy output to total energy input, expressed as a percentage: (12 500 J ÷ 50 000 J) × 100 % = 25 %.
Examiner tips
- Use the exact terminology: chemical energy, kinetic energy, thermal/heat energy, sound energy, efficiency. Include the calculation of 25 %.
- Show the efficiency formula and the percentage result. Keep the answer concise and to the point.
Mark scheme (4 marks)
- Chemical energy in the fuel is the input energy store / source
- Useful energy transfer is to the kinetic energy store of the go-kart
- Waste energy transfers include thermal/heat energy (due to friction / engine heating) and/or sound energy
- Efficiency is the ratio of useful energy output to total energy input (× 100 %); here 12 500 / 50 000 = 25 %
Key terms in this question
chemical energy · kinetic energy · useful energy transfer · waste energy transfer · efficiency
Related
- All Pearson Edexcel International GCSE Physics (4PH1) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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