A hollow iron pipe is 21 cm long with external diameter 8 cm and thickness 1 cm. If the density of iron is 8 g/cm^3, what is the weight of the pipe?

Problem Restatement

Compute mass of a hollow cylindrical shell from its geometric volume and material density.

Given data

• Length, L = 21 cm
• External diameter = 8 cm → R = 4 cm
• Thickness = 1 cm → inner radius r = 3 cm
• Density ρ = 8 g/cm^3

Concept / Formula

• Volume of material (hollow cylinder): V = πL(R^2 − r^2)
• Mass = ρV

Step-by-step calculation

V = π × 21 × (4^2 − 3^2) = π × 21 × 7 = 147π cm^3Using π = 22/7 → V = 147 × 22/7 = 462 cm^3Mass = 8 × 462 = 3696 g = 3.696 kg

Final Answer

Weight of the pipe ≈ 3.696 kg.