Checkpoint 1, Energy Conservation
In 2023, CSIRO's solar thermal test rig achieved 750 °C, applying every concept from this checkpoint in one real system.
Printable Worksheets
Print or save as PDF, or build a custom worksheet from any module's questions.
Lessons 1–10 covered the core physics of energy. You explored how energy cannot be created or destroyed, only transformed, and how we track those transformations through calculations, Sankey diagrams, and efficiency values. You also studied the three heat transfer mechanisms (conduction, convection, radiation) and the properties of specific heat capacity and thermal expansion that determine how materials respond to temperature change.
"A ball at the bottom has more total energy than at the top."
Total mechanical energy is conserved (ignoring friction). GPE converts to KE, total stays the same.
"90% efficient means it wastes 90%."
90% efficient means 90% is USEFUL, only 10% is wasted.
"Holding a box still does work because it's heavy."
Work = Force × distance. No movement = no work done.
"Wider waste arrow in a Sankey diagram means more efficiency."
Wider waste arrow = MORE wasted energy = LOWER efficiency.
- Conservation of energy
- Efficiency
- Sankey diagram
- Conduction
- Specific heat capacity
- Diagram showing energy flow, arrow width = energy amount
- Energy cannot be created or destroyed, only transformed
- Energy needed to raise 1 kg of substance by 1°C
- Useful energy out divided by total energy in × 100%
- Heat transfer through direct contact between particles
At the start of Lessons 1–10, you were new to energy conservation. Now that you have worked through the full checkpoint, reflect on your understanding. Which concept clicked most for you? Which still feels uncertain?
Q1. 6. Draw a simple Sankey diagram for a device with 800 J input, 200 J useful output, and 600 J waste. Use a scale of 1 cm = 100 J. Label all arrows with energy values, forms, and units. Calculate and state the efficiency.
1 mark for correct arrow widths (8 cm, 2 cm, 6 cm). 1 mark for labels with values, forms and units. 1 mark for efficiency = 25%.Q2. 7. A family is choosing between two kettles. Kettle A is 2,000 W and boils 1 litre of water in 3 minutes. Kettle B is 1,000 W and boils the same amount in 6 minutes. Both are 90% efficient.
1 mark for calculating energy for Kettle A (360,000 J or 0.1 kWh). 1 mark for calculating energy for Kettle B (360,000 J or 0.1 kWh). 1 mark for explaining that both use the same energy but Kettle A is faster. 1 mark for cost calculation and recommendation with reasoning.Q3. 8. The Nullarbor Plain in South Australia has summer temperatures of 50°C and winter temperatures of 5°C. A new railway is being built across the plain. Engineers must decide between jointed track (with gaps) and continuously welded rail (no gaps).
1 mark for calculating or describing the temperature range (45°C) and its effect on steel expansion. 1 mark for explaining how jointed track works (gaps allow expansion, prevent buckling). 1 mark for explaining how welded rail works (constrained expansion, requires resistance to buckling). 1 mark for evaluating specific Nullarbor challenges (extreme heat, remote location, maintenance access). 1 mark for justified recommendation with physics reasoning.Model answers (click to reveal)
Comprehensive Answers
▼Multiple Choice
1. BUseful = 1,000 × 0.35 = 350 MJ. Waste = 1,000 − 350 = 650 MJ.
2. CWater at height has GPE → falls and gains KE → spins turbines → generates electrical energy.
3. AForce = 30 × 10 = 300 N. Work = 300 × 2 = 600 J. The student used mass instead of force.
4. DSand c ≈ 800 J/kg°C, water c = 4,200 J/kg°C. Same energy input: sand heats ~5× more.
5. BConcrete expands when heated. Without gaps, compressive stress causes buckling.
Short Answer Model Answers
Q6 (3 marks): Input arrow: 8 cm wide, labelled "800 J chemical energy" [0.5]. Useful output: 2 cm wide, labelled "200 J useful energy" [0.5]. Waste: 6 cm wide, labelled "600 J waste thermal energy" [0.5]. Scale stated: 1 cm = 100 J [0.5]. Efficiency = (200 ÷ 800) × 100 = 25% [1 mark].
Q7 (4 marks): (a) Kettle A: 2,000 W × 180 s = 360,000 J (0.1 kWh) [0.5]. Kettle B: 1,000 W × 360 s = 360,000 J (0.1 kWh) [0.5]. (b) Both use the same energy because they heat the same water [0.5]. Kettle A is more powerful, doing the same work in half the time [0.5]. Cost: both = 0.1 × $0.30 = $0.03 per boil [0.5]. Recommendation: Kettle A for busy households where speed matters; Kettle B for energy-conscious users on a budget (lower upfront cost) [0.5].
Q8 (5 marks): Temperature range = 50 − 5 = 45°C [0.5]. Steel rails expand by approximately 5.4 mm per 10 m per 45°C [0.5]. Jointed track: Gaps allow free expansion, eliminating buckling risk [0.5]. Disadvantages: noise, vibration, higher maintenance, speed restrictions [0.5]. Welded rail: Smoother ride, lower long-term maintenance, higher speeds [0.5]. Disadvantages: requires massive concrete sleepers to resist buckling; extreme heat (50°C) creates enormous compressive forces [0.5]. Nullarbor challenges: Remote location makes maintenance difficult; extreme heat increases buckling risk; 45°C range is among the highest in Australia [0.5]. Recommendation: Jointed track for the Nullarbor [0.5]. Justification: the extreme temperature range and remote location make maintenance-critical. Jointed track fails safely (gaps widen) and is easier to repair in isolated areas. Welded rail would require constant monitoring and speed restrictions on extreme heat days, which is impractical 500 km from the nearest town [0.5].
📚 Revisit the Content
Want to review any section before moving on?