WAEC Physics 2024 Paper

Concept:Apply Archimedes' principle: a floating object displaces its own weight of fluid.Explanation:The cube has side length $10.0$ cm, so its total volume is:$V = s^3 = 10^3 = 1000$ cm$^3$Only $4.5$ cm of the cube's length is submerged.The submerged volume is:$V_{\text{sub}} = 10 \times 10 \times 4.5 = 450$ cm$^3$The volume of water displaced equals the submerged volume, $450$ cm$^3$.Mass of water displaced:$m = \rho_{\text{water}} \times V_{\text{sub}} = 1 \times 450 = 450$ gFor a floating object, the mass of the cube equals the mass of water displaced.So, mass of cube $= 450$ g.Density of the cube:$\rho_{\text{cube}} = \frac{\text{mass}}{\text{volume}} = \frac{450}{1000} = 0.45$ g/cm$^3$Answer:The density of the wood is $0.45$ g/cm$^3$, which is option B.