JAMB Physics 2020 Paper

Concept:Density ratios are found using Archimedes' principle. Loss of weight in a liquid equals the weight of the liquid displaced.Explanation:Weight of solid in air $= 4.8\,g$. Weight of solid in water $= 2.8\,g$. Weight of solid in kerosine $= 3.2\,g$. Loss of weight in water $= 4.8 - 2.8 = 2.0\,g$. This equals the weight of an equal volume of water. So relative density of the solid $= \frac{4.8}{2.0} = 2.4$. Loss of weight in kerosine $= 4.8 - 3.2 = 1.6\,g$. This equals the weight of kerosine displaced by the solid. Weight of the same volume of water is $2.0\,g$. Therefore, relative density of kerosine $= \frac{1.6}{2.0} = 0.8$. Density is directly proportional to relative density, so: $\frac{\text{density of solid}}{\text{density of kerosine}} = \frac{2.4}{0.8} = 3$.Answer:D. 3