Fluid Properties MCQ with answer and solution

Concept

Mass density is mass per unit volume, and mass = weight / g.

Formula

m = W / g ; ρ = m / V

Step-by-step solution

1. Weight W = 40 kN = 40000 N 2. Mass m = W / g = 40000 / 10 = 4000 kg 3. Volume V = 4.5 m³ 4. Density ρ = m / V = 4000 / 4.5 = 888.9 kg/m³ ≈ 889 kg/m³

Explanation

First change the weight into mass by dividing by g. Then divide the mass by the volume. This gives about 889 kg/m³.

Why the other options are wrong

B (809) and D (850) come from calculation errors. C (920) is a typical oil density value, but it does not match this data.

Shortcut

ρ = W / (g × V) = 40000 / (10 × 4.5) = 889 kg/m³

Common mistake

Dividing weight by volume gives specific weight (8889 N/m³), not mass density. Forgetting to change kN to N is another error.