A student places a solid rubber bung into a measuring cylinder containing water. The water level rises from 40 cm³ to 55 cm³. The student then measures the mass of the rubber bung using a balance and finds it to be 22.5 g. Explain how the student uses these measurements to determine the density of rubber, and state the value of the density.

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)

The volume of the rubber bung is the increase in water level:

V = 55 cm³ – 40 cm³ = 15 cm³.

Density is mass divided by volume:

ρ = m ÷ V = 22.5 g ÷ 15 cm³ = 1.5 g cm⁻³.

Thus the density of the rubber is 1.5 g cm⁻³ (≈1500 kg m⁻³).

Examiner tips

  • Show the subtraction to find volume first, then write the density formula and substitute the numbers.
  • Include the units in the final answer to demonstrate correct calculation.

Mark scheme (4 marks)

  1. Volume of rubber bung is found by subtracting the initial water level from the final water level (55 − 40 = 15 cm³)
  2. Density is calculated using density = mass ÷ volume
  3. Correct substitution of values: density = 22.5 ÷ 15
  4. Correct density value of 1.5 g/cm³ (or equivalent 1500 kg/m³)

Key terms in this question

density · mass

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