Question

A stone of mass 10 kg is lying at the bed of a lake 5 m deep. If the relative density of the stone is 2, the amount of work done to bring it to the top of the lake will be:

Answer 1

Hey

Relative Density of stone = 2
--> Density of stone = 2 * 1000kg / m^3

--> Mass of stone = 10kg
--> Volume of stone = ( 1 / 200 )m^3

Now,
Net force acting = Gravitational force - Buoyant Force

=> F(stone) = 10 * 9.8 - ( 1/200 ) * 1000 * 9.8
= 98 - 49 = 49 N

Hence, 49N force is acting on the stone.
.'. To bring it back up, a net of -49N force has to be applied..

Depth = 5m

So, Work done in bringing it back = 49*5
=> Work done = 245J ✓✓

Hope it helps ^_^