A shot-put is a metallic sphere of radius 4.9 cm. If the density of the metal is 7.8 g per cm³, find the mass of the shot-put.

Volume of sphere = $\dfrac{4}{3}πr^3$

Putting values in equation we get,

$\text{Volume of sphere } = \dfrac{4}{3} \times \dfrac{22}{7} \times (4.9)^3 \\[1em] = \dfrac{4 \times 22 \times 117.649}{21} \\[1em] = \dfrac{10353.112}{21} \\[1em] = 493 \text{ cm}^3.$

Since, the density of the metal is 7.8 g per cm³.

Mass = Volume × Density.

So, the mass of the metallic sphere 493 × 7.8 = 3845441.6 g

= $\dfrac{3845441.6}{1000}$ = 3.845 kg.

Hence, the mass of the metallic sphere is approx 3.85 kg.