Gravitation MCQs

Q1. During a school laboratory session a metallurgist weighs a block of aluminium and finds its density to be 2.7 g/cm^3, while the jar of water on the same bench reads 1 g/cm^3; what relative density does the aluminium have?

• A.2.7 g/cm^3
• B.3.7
• C.2.7
• D.0.3704

Answer: C. 2.7

Relative density = density of substance / density of water = 2.7 g/cm^3 / 1 g/cm^3 = 2.7. It is a ratio of two densities, so it has no units.

Q2. At an antique fair a chemistry student inspects an ingot cast from iron and measures its density as 7.8 g/cm^3, comparing it against a beaker of water at 1 g/cm^3; what is the relative density of the iron?

• A.7.8
• B.7.8 g/cm^3
• C.0.1282
• D.8.8

Answer: A. 7.8

Relative density = density of substance / density of water = 7.8 g/cm^3 / 1 g/cm^3 = 7.8. It is a ratio of two densities, so it has no units.

Q3. Inside a workshop a jeweller clamps a rod of copper and records a density of 8.9 g/cm^3, then notes the tap water nearby at 1 g/cm^3; what value of relative density follows for the copper?

• A.9.9
• B.0.1124
• C.8.9
• D.8.9 g/cm^3

Answer: C. 8.9

Relative density = density of substance / density of water = 8.9 g/cm^3 / 1 g/cm^3 = 8.9. It is a ratio of two densities, so it has no units.