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Fluid flow

Free AQA GCSE Physics practice questions on Fluid flow. Sample questions below with detailed mark schemes — sign up to practise the full set with spaced repetition.

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Explain — 3 marks

A water pipe system supplies water to a village. The pipe narrows at one section before widening again further downstream. Engineers notice that the water flows faster in the narrow section than in the wide sections.

  1. Explain why the water flows faster in the narrow section of the pipe. [1 mark]
  2. The pressure in the water is lower in the narrow section than in the wide sections. Explain why. [1 mark]
  3. The same volume of water passes through every section of the pipe each second. Explain what this tells us about the relationship between the cross-sectional area of the pipe and the speed of fluid flow. [1 mark]
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Explain — 3 marks

A water treatment plant uses pipes of different diameters to transport water at different stages of the filtration process. Engineers notice that the water flows more slowly through wider pipes and faster through narrower pipes, even though the same volume of water enters and leaves each section per second.

  1. Explain why the water flows at different speeds in pipes of different diameters. [1 mark]
  2. The continuity equation for fluid flow states that A₁v₁ = A₂v₂, where A is the cross-sectional area and v is the velocity. Using this relationship, explain what happens to the velocity when the cross-sectional area of the pipe doubles. [1 mark]
  3. At one point in the treatment process, the pipe narrows from a diameter of 10 cm to a diameter of 5 cm. Explain the relationship between the change in pipe diameter and the change in water velocity, using the concept of conservation of mass. [1 mark]
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Show — 2 marks

A garden hose is used to fill a water tank. When the tap is fully open, water flows quickly out of the hose. When the tap is partially closed, the water flows more slowly.

  1. Show that the volume of water flowing through the hose depends on both the cross-sectional area of the hose and the speed of the water. [2 marks]
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  • {'mark': 1, 'description': 'States that volume flow rate equals cross-sectional area multiplied by fluid speed (Q = A × v or equivalent)'}
  • {'mark': 1, 'description': 'Explains that increasing either the cross-sectional area OR the speed of water increases the volume of water flowing per unit time'}

State — 4 marks

A water treatment plant uses pipes of different diameters to transport water at constant volume flow rate through the system. Engineers need to understand how the water's speed changes as it moves through sections of pipe with different cross-sectional areas.

  1. State the equation that links volume flow rate, cross-sectional area, and fluid velocity. [1 mark]
  2. Water flows through a pipe at a constant volume flow rate of 0.12 m³/s. The pipe narrows from a cross-sectional area of 0.08 m² to 0.02 m². State what happens to the velocity of the water as it enters the narrower section. [1 mark]
  3. State two reasons why understanding fluid flow is important for the design and operation of water distribution systems. [2 marks]
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