Question

The work done in lifting a body of mass 20kg and specific gravity 3.2 to a height of 8m in water is? (g = 10m/s-2)

Answer 1

The mass of the water that will be displaced by body is $\frac{20}{3.2}=6.25\text{kg}$
So the downwards force on the body due to gravity is $20\times 10=200\text{N}$
and upward force by water is $6.25\times 10=62.5\text{N}$
Hence total force is $200-62.5=137.5\text{N}$
Hence the work done to lift the mass to 8 m is $137.5\times 8=1100\text{J}$