Question

Calculate work done in raising a stone of mass 5kg and specific gravity 3 lying at the bed of a lake through a height of 4 metre.

Answer 1

Here,`m=5kg`, sp. Gravity `=3,h=4m,W=?`
As specify gravity of stone
`=("mass of stone in air")/("mass of an equal volume of water")`
`:. 3=(5kg)/(m) :. m=(5)/(3)kg`
Loss of weight of stone when immersed in water
= Weight of water displaced `=(5)/(3)kg`
Apparent weight of stone in water
`=(5-(5)/(3))kg=(10)/(3)kg`
Force required to lift the stone, `F=(10)/(3)xx9.8N`
Work done `=Fxxh=(10)/(3)xx9.8xx4=130.7J`