Density (AQA A Level Physics): Revision Note

A paving slab has a mass of 73 kg and dimensions 40 mm × 500 mm × 850 mm.

Calculate the density, in kg m^-3 of the material from which the paving slab is made.

[3]

Answer:

Step 1: Calculate the volume of the slab

$40\mathrm{mm}=0.04\mathrm{m}$

$500\mathrm{mm}=0.50\mathrm{m}$

$850\mathrm{mm}=0.85\mathrm{m}$

$V=0.04\times 0.50\times 0.85=0.017{\mathrm{m}}^3$ [1 mark]

Step 2: Calculate the density of the slab

$\rho =\frac{m}{V}=\frac{73}{0.017}$ [1 mark]

$\rho =4294\mathrm{kg}{\mathrm{m}}^{-3}=4300\mathrm{kg}{\mathrm{m}}^{-3}\left(2\mathrm{s}.\mathrm{f}.\right)$ [1 mark]

• When converting a larger unit to a smaller one, you multiply (×)

  • E.g. 125 m = 125 × 100 = 12 500 cm

• When you convert a smaller unit to a larger one, you divide (÷)

  • E.g. 5 g = 5 / 1000 = 0.005 or 5 × 10^-3 kg

• When dealing with squared or cubic conversions, cube or square the conversion factor too

  • E.g. 1 mm³ = 1 / (1000)³ = 1 × 10^-9 m³

  • E.g. 1 cm³ = 1 / (100)³ = 1 × 10^-6 m³