Question:
A wooden cylindrical pole is 7 m high and its base radius is 10 cm. Find its weight if the wood weighs 225 kg per cubic metre.
Solution:
Height $=7 \mathrm{~m}$
Radius $=10 \mathrm{~cm}=0.1 \mathrm{~m}$
Volume $=\pi \mathrm{r}^{2} \mathrm{~h}=\frac{22}{7} \times 0.1 \times 0.1 \times 7=0.22 \mathrm{~m}^{3}$
Weight of wood $=225 \mathrm{~kg} / \mathrm{m}^{3}$
$\therefore$ Weight of the pole $=0.22 \times 225=49.5 \mathrm{~kg}$