A hollow spherical shell is made of a metal of density 7 g/cm³. Its internal and external radii are 0 cm and 3 cm, respectively. What is the approximate weight (in kg) of the shell?
$$\left( \text{Take } \pi = \frac{22}{7}, \text{ Density} = \frac{\text{Mass}}{\text{Volume}} \right)$$​

Correct option is C

Given:

Shape: Hollow spherical shell

Internal radius = 0 cm

External radius = 3 cm

Density = 7 g/cm³

Formula Used:

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

Mass = Density × Volume

Convert grams to kilograms: 1 kg = 1000 g

Solution:

Volume of hollow sphere = $$\frac{4}{3} \times \frac{22}{7} \times 3^3$$​​

= $$\frac{4}{3} \times \frac{22}{7} \times 27$$​​

= $$\frac{4 \times 22 \times 27}{3 \times 7}$$​​

= $$\frac{792}{7}$$​ cm³

Mass = Volume × Density =$$\frac{792}{7}$$ × 7 = 792 grams​

Convert to kg:

792 ÷ 1000 = 0.792 kg