A large water storage tank is used to supply water to a building. The tank is positioned on the roof of the building. Explain why water flows out more quickly from a tap on the ground floor than from a tap on the top floor, just below the tank.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Pressure in a fluid increases with depth. The ground floor tap is deeper below the water surface in the tank than the top floor tap. Therefore the pressure at the ground floor tap is greater than at the top floor tap. The higher pressure forces the water to flow out more quickly from the ground floor tap.
Examiner tips
- Use the phrase ‘pressure increases with depth’ to show understanding of hydrostatic pressure.
- Explain the relative depths of the two taps before linking to pressure difference.
- State that greater pressure gives greater flow rate or force.
- Keep the answer concise – 4 marks can be earned with a short paragraph.
Mark scheme (4 marks)
- Pressure in a fluid increases with depth (or greater depth means greater pressure)
- The ground floor tap is at a greater depth below the surface of the water in the tank than the top floor tap
- So the water pressure at the ground floor tap is greater than at the top floor tap
- Greater pressure causes the water to flow out faster / with greater force
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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