A large wooden storage crate and a small metal toolbox are both resting on a soft muddy ground. The wooden crate has a greater weight than the metal toolbox, yet the wooden crate sinks less deeply into the mud. Explain why the wooden crate sinks less deeply into the mud than the metal toolbox.

Pearson Edexcel International GCSE Physics (4PH1) — 5.1 Density and pressure · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

The base area of the wooden crate is much greater than the base area of the metal toolbox.

Model answer (4 marks)

Pressure is force per unit area (p = F/A). The wooden crate has a much larger base area in contact with the mud than the metal toolbox. For the same weight (force) the larger area gives a lower pressure on the mud. The mud reacts with a smaller upward force, so the crate does not sink as far into the mud.

Examiner tips

  • State the definition of pressure and use p = F/A
  • Explain that the crate’s larger base area reduces pressure
  • Show the link between lower pressure and less sinking
  • Use clear, concise language

Common mistakes

  • Confusing weight with mass
  • Ignoring the base area difference
  • Using the wrong equation for pressure

Mark scheme (4 marks)

  1. Pressure is defined as force per unit area (or p = F/A)
  2. The wooden crate has a much larger base area in contact with the mud
  3. Because the area is greater, the pressure exerted on the mud is lower (for the wooden crate)
  4. Lower pressure on the mud means the mud exerts less of a reaction/the crate does not sink as far into the mud

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