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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.
Solution
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
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