🔬 Part 1: Basic Calculations
Formula: W = p × ∆V (where W = work done in J, p = pressure in Pa, ∆V = change in volume in m³)
Success Criteria: Correctly substitute values into the formula and calculate work done with appropriate units.
1. A gas at constant pressure of 2000 Pa expands from 0.5 m³ to 1.2 m³. Calculate the work done by the gas.
2. Calculate the work done when a gas at 150,000 Pa pressure compresses from 0.8 m³ to 0.3 m³.
3. A gas does 4500 J of work whilst expanding by 0.15 m³. What is the pressure of the gas?
4. At what volume will a gas finish expanding if it starts at 0.2 m³, has a pressure of 80,000 Pa, and does 12,000 J of work?
🧠 Part 2: Conceptual Understanding
Success Criteria: Demonstrate understanding of the relationship between pressure, volume change, and work done.
5. When is work done by a gas rather than on a gas?
When the gas expands
When the gas is compressed
When pressure increases
When temperature decreases
6. What happens to the work done if the pressure doubles but the volume change stays the same?
Work done halves
Work done doubles
Work done stays the same
Work done becomes zero
7. Explain why work done is positive when a gas expands and negative when it compresses.
8. A gas expands at constant pressure. Sketch a pressure-volume graph and shade the area representing work done.
🚀 Part 3: Real-World Applications & Extension
Success Criteria: Apply gas work calculations to practical scenarios and solve multi-step problems.
9. A car engine cylinder contains gas at 500,000 Pa. During the power stroke, the gas expands from 50 cm³ to 400 cm³. Calculate the work done. (Remember to convert units!)
10. A steam engine operates with steam at 200,000 Pa pressure. If the piston moves to increase the cylinder volume by 0.025 m³, how much work is done by the steam?
11. Extension: A gas undergoes a cycle where it first expands from 0.1 m³ to 0.4 m³ at 100,000 Pa, then is compressed back to 0.1 m³ at 50,000 Pa. Calculate the net work done in the complete cycle.
12. Extension: Research and explain how the work done by gases is utilised in one of the following: refrigeration systems, pneumatic tools, or jet engines.
📝 Answer Key
1. 1400 J
2. -75,000 J
3. 30,000 Pa
4. 0.35 m³
5. When the gas expands
6. Work done doubles
7. Work is positive during expansion because the gas does work ON the surroundings by pushing against external pressure. Work is negative during compression because work is done ON the gas by external forces, requiring energy input to reduce the gas volume.
8. Graph should show: horizontal line (constant pressure), volume increasing from left to right, rectangular area under the line shaded to represent work done.
9. 175 J
10. 5000 J
11. 15,000 J
12. Pneumatic tools use compressed air to do work. When compressed air expands rapidly in the tool's cylinder, it does positive work by moving pistons or rotors. This work is transferred to the tool's mechanism to perform useful tasks like drilling or breaking concrete.
