Question

Find the weight of a hollow sphere of metal having internal and external diameters as 20 cm and 22 cm, respectively if 1m³ of metal weighs 21g.

Answer 1

External radius of hollow sphere, \[r_1 = \frac{22}{2}\] 11 cm

Internal radius of hollow sphere, `r_2 = 20/2`= 10 cm

The volume of hollow sphere =  \[\frac{4}{3}\pi\left( {r_1}^3 - {r_2}^2 \right)\]

`=4/3 pi (11^3 - 10^3)`

`=4/3 pi xx 331`

`= (1324 xx 22)/21`

The volume of hollow sphere`= (1324 xx 22)/21`

The weight of hollow sphere `= (1324 xx 22)/21 xx 21gm` 

= 29128 gm

= 29.13 kg