Page 126 - Science Coursebook

9.3 Density calculations

Here is the equation which is used to calculate the density of a material, written in
words and in symbols:
mass
density =
volume
M
D =
V
where D = density, M = mass, V = volume.

Question
A+I 1 A rectangular block of steel measures 4 cm × 2 cm × 1.5 cm. Its mass is 93.6 g.
a Calculate the density of steel.
b Steel is made almost entirely of iron atoms, but it is denser than iron.
Suggest a reason for this.

Calculating mass
We can rearrange the equation for density like this:

mass = density × volume
M = D × V

A fish tank.
Example: A fish tank measures 80 cm × 20 cm × 25 cm. It is to be filled with

water, density 1.0 g/cm . Calculate the mass of water in the tank when it is full.
3
Step 1: Calculate the volume of the tank.
volume = length × width × height = 80 × 20 × 25 = 40 000 cm 3
Step 2: Calculate the mass of the water.
mass = density × volume = 40 000 × 1.0 = 40 000 g

Question
2 A half litre bottle has a mass of 80 g. It contains 500 cm
3

of liquid when full. The bottle is filled with olive oil of
density = 0.90 g/cm .
3
a Calculate the mass of oil in the bottle.
b Calculate the mass of the full bottle.

Calculating volume
We can rearrange the equation for density to make volume its subject,
like this:
mass
volume =
density
M
V =
D A bottle of oil.

124 9 Forces in action