The external and interenal diameter of a hollow copper-sphere are 20 cm and 16 cm respectively . By melting this sphere, how many solid bullets of diameter 4 cm each can be made?

Explanation

The external radius of the hollow sphere `=(20)/(2)`cm=10.
and the internal radius of the hollow-sphere `=(16)/(2) `cm =8 cm.
`therefore` the volume of materials of the hollow sphere
`=[(4)/(3)pixx10^(3)-(4)/(3)pixx8^(3)]cc.=(4)/(3)pi(1000-512)cc=(4)/(3)pixx488cc`
The radius solid bullets `=(4)/(2)` cm =2 cm
`:.` volume of solid bullets `=(4)/(3)pixx2^(3)` cc.
Let the number of solid bullets that can be made be x.
`:. x xx (4)/(3)pixx2^(3)=(4)/(3)pixx(488)/(8) = 61.`
Hence 61 solid bullets can be made.