A metallic sphere with an internal cavity weighs `40 gwt` in air and `20 gwt` in water. If the density of the material with cavity be `8g per cm^(3)` then the volume of cavity is :

Options

A. zero
B. `15cm^(3)`
C. `5cm^(3)`
D. `20cm^(3)`

Answer

B

Explanation

Weight of sphere in air `=40kg`
Weight of sphere in water `=20g`
Loss in weight `=(40-20)g=20g`
Weight of water displaced `=` loss in weight `=20`g
Volume of water displaced `=20cm^(3)`
Actual volume of sphere `=` volume of water displaced `=20cm^(3)`
Volume of material displaced `=20cm^(3)` Actual volume of sphere `=(40)/(8)=5cm^(3)`
Actual volume of sphere `=` volume of water displaced `=20cm^(3)`
Volume of material in sphere `=(40)/(8)=5cm^(3)`
Volume of cavity `=(20-5)=15cm^(3)`