Question:
A solid cube of metal each of whose sides measures 2.2 cm is melted to form a cylindrical wire of radius 1 mm. Find the length of the wire so obtained.
Solution:
Length of the edge, $a=2.2 \mathrm{~cm}$
Volume of the cube $=a^{3}=(2.2)^{3}=10.648 \mathrm{~cm}^{3}$
Volume of the wire $=\pi \mathrm{r}^{2} \mathrm{~h}$
Radius $=1 \mathrm{~mm}=0.1 \mathrm{~cm}$
As volume of cube = volume of wire, we have:
$h=\frac{\text { volume }}{\pi \mathrm{r}^{2}}=\frac{10.648 \times 7}{22 \times 0.1 \times 0.1}=338.8 \mathrm{~cm}$