Calculate its density
Density — Notes & Worked Examples Show / Hide
Explanation:
Density, mass and volume are linked by Density = MassVolume, Mass = Density × Volume, and Volume = MassDensity. Check the units carefully: if density is in g/cm3, mass must be in grams (1 kg = 1000 g) and volume in cm3.
When two metals or liquids are mixed together, never average the two densities—always work out the Total Mass and Total Volume separately, then use Combined Density = Total MassTotal Volume.
Example 1: A solid metal block has volume 350 cm3 and density 8.4 g/cm3. Find its mass in kilograms.
Solution:
Example 2: Liquid A (180 g, density 0.9 g/cm3) is mixed with Liquid B (420 g, density 1.4 g/cm3). Find the density of the mixture.
Solution:
Calculate its density
Calculate its mass
Worked Solution & Answer
Solid **A** has a mass of 2000 g
Solid **B** has a mass of 3375 g
Solid **B** has a volume of 450 cm3
All of the metal from Solid **A** and Solid **B** is melted down to make a uniform Solid **C**
Given that there is no change to mass or volume during this process
work out the density of Solid **C**
Give your answer correct to one decimal place.
Worked Solution & Answer
Volume of Solid A = π × 32 × 7 = 63π ≈ 197.92 cm3 M1
Total mass = 2000 + 3375 = 5375 g M1
Total volume = 63π + 450 ≈ 647.92 cm3
Density = 5375 ÷ 647.92 = 8.2957... = 8.3 g/cm3. A1
The mass of the cylinder is 7.04 kg
Work out the density of the iron.
Give your answer in g/cm3 correct to 2 significant figures.
Worked Solution & Answer
Volume = π × 9² × 3.5 = 283.5π ≈ 890.64 cm³ M1
Mass = 7040 g M1
Density = 7040 ÷ 890.64 = 7.904… = 7.9 g/cm³ (2 s.f.) A1
The density of iron is 7.8 g/cm3
The mass of the block is 1950 g
Work out the value of w
Worked Solution & Answer
Volume = Mass ÷ Density = 1950 ÷ 7.8 = 250 cm³ M2
5 × 4 × w = 250 ⇒ 20w = 250 ⇒ w = 12.5 A1
Cube **B** has a mass of 128 g.
Work out
[INDENT]the density of cube **A** : the density of cube **B**
Give your answer in the form a : b, where a and b are integers.
Worked Solution & Answer
Volume A = 3³ = 27 cm³ ⇒ density A = 81 ÷ 27 = 3 g/cm³ M1
Volume B = 4³ = 64 cm³ ⇒ density B = 128 ÷ 64 = 2 g/cm³ M1
Ratio = 3 : 2 A1
The cylinder has radius 8 cm and height h cm.
The volume of the cylinder is 1208 cm3
Give your answer correct to the nearest whole number. [2 marks]
Give your answer in kilograms. [2 marks]
Worked Solution & Answer
π × 8² × h = 1208 M1
⇒ h = 1208 ÷ (64π) = 6.008... ≈ 6 A1
Mass = 1208 × 1.25 = 1510 g = 1.51 kg M1 A1
(a) A solid block of wood is a cuboid which measures 3 cm by 4 cm by 5 cm.
Its density is 0.65 g/cm3.
Work out the mass of the block of wood.
(b) Here are two areas.
Its density is 0.65 g/cm3.
Work out the mass of the block of wood. [2 marks]
Show how you decide.
Worked Solution & Answer
Mass = density × volume = 0.65 × 60 = 39 g. A1
1 m² = 1000² mm² = 1 000 000 mm². M1
0.12 m² = 120 000 mm² > 95 000 mm² (or 95 000 mm² = 0.095 m² < 0.12 m²), so Area A is greater. C1
He melted down some gold blocks and used the gold to make the statue.
Each block of gold was a cuboid, as shown below.
The density of gold is 19.32 g/cm3
Work out the least number of gold blocks Pablo melted down in order to make the statue.
Show your working clearly.
Worked Solution & Answer
Volume of 1 block = 1.5 × 2 × 8 = 24 cm³ M2
Mass of 1 block = 24 × 19.32 = 463.68 g M2
Number of blocks = 5730 ÷ 463.68 = 12.357... ⇒ 13 blocks A1
The mass of X is 10.976 kg
The area of **each face** of X is 784 cm2
He assumes that Y is identical to X.
What density should he get for Y?
Give your answer in **grams per cubic centimetre**. [4 marks]
the mass of Y is less than the mass of X
the area of each face of Y is greater than the area of each face of X.
What does this mean about the actual density of Y?
Tick **one** box.
[ ] It is less than the answer to part (a)
[ ] It is equal to the answer to part (a)
[ ] It is greater than the answer to part (a)
[ ] It is not possible to tell [1 mark]
Worked Solution & Answer
Side length of X = √784 = 28 cm M1
Volume of X = 28³ = 21 952 cm³ M1
Mass in grams = 10.976 × 1000 = 10 976 g M1
Density = 10 976 ÷ 21 952 = 0.5 g/cm³ A1
Smaller mass divided by a larger volume gives a smaller density B1