If 1 cm3 of case iron weighs 21 g, find the weight of a cast iron pipe of length

Internal radius of the pipe = 1.5 cm
External radius of the pipe = (1.5 + 1) cm = 2.5 cm
Height of the pipe = 1 m = 100 cm
Volume of the cast iron = total volume of the pipe − internal volume of the pipe

$=\pi \times(2.5)^{2} \times 100-\pi \times(1.5)^{2} \times 100$

$=\frac{22}{7} \times 100 \times[6.25-2.25]$

$=\frac{2200}{7} \times 4=\frac{8800}{7} \mathrm{~cm}^{3}$

1 cm3 of cast iron weighs 21 g.

$\therefore$ Weight of $\frac{8800}{7} \mathrm{~cm}^{3}$ cast iron $=\frac{8800}{7} \times \frac{21}{1000} \mathrm{~kg}=88 \times 0.3=26.4 \mathrm{~kg}$