**Question:**

Find the length of 13.2 kg of copper wire of diameter 4 mm, when 1 cubic cm of copper weighs 8.4 gm.

**Solution:**

Since we know the weight and the volume of copper, we can calculate its density.

density of copper $=\frac{\text { weight }}{\text { volume }}=\frac{8.4 \mathrm{gram}}{1 \mathrm{~cm}^{3}}=8.4 \frac{\mathrm{gram}}{\mathrm{cm}^{3}}$

If the weight of copper wire is 13.2 kg and the density of copper is 8.4 g/cm3, then:

Volume = Weight / Density = 13.2 kg x 1000 gram/kg / 8.4 gram/cm3 = 1571.43 cm3

The radius of copper wire is 2 mm or 0.2 cm. So, the length of the wire can be determined in the following way:

$\mathrm{L}=\frac{\mathrm{V}}{\pi r^{2}}=\frac{1571.43 \mathrm{~m}^{3}}{\pi(0.2 \mathrm{~cm})^{2}}=125050.01 \mathrm{~cm}=125 \mathrm{~m}$

Thus, the length of 13.2 kg of copper is 125 m.