A copper sphere of diameter 18 cm is drawn into a wire of diameter 4 mm. The length of the wire, in metre, is

Volume of sphere $=\frac{4}{3} \pi r^{3}$

$=\frac{4}{3} \pi \times 9 \times 9 \times 9=972 \pi$ cubic.cm.

If the length of wire be $\mathrm{h} \mathrm{cm}$., then $\pi \times(0.2)^{2} \times h=972 \pi$

$\Rightarrow h=\frac{972}{0.2 \times 0.2}=24300 \mathrm{~cm}=243$ metres