A fishing weight is made from lead and a fishing float is made from cork. Both objects have the same mass. Explain why the fishing float has a much larger volume than the fishing weight.

Cambridge International IGCSE Physics (0625) — 1.4 Density · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Density is mass per unit volume.
Lead has a much higher density than cork.
Since both objects have the same mass, the object with the lower density must have a larger volume.
Cork (the float) has a low density, so a large volume is needed to account for the same mass as the much denser lead weight.

Examiner tips

  • Use the definition of density first. Compare the densities of lead and cork. Explain the inverse relationship between density and volume for equal mass. Show the logical chain clearly.

Common mistakes

  • Confusing density with mass. Saying the float is lighter instead of having a larger volume. Not linking the same mass to the need for a larger volume.

Mark scheme (4 marks)

  1. Density is defined as mass per unit volume
  2. Lead has a much higher density than cork
  3. Since both objects have the same mass, the object with lower density must have a larger volume
  4. Cork (the float) has a low density, so a large volume is needed to account for the same mass as the much denser lead weight

Key terms in this question

mass · volume

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