The radius of a well is 7m. Water in it is at a depth of 20m and depth of water column is 10m. Work done in pumping out water completely from the well is, (g = 10ms^–2)

Let total mass of water be m,

$mass=density\times volume$

$m=1000\times {\mathrm{\pi R}}^2\mathrm{h}$

$\mathrm{m}=1000\times \frac{22}{7}\times 7^2\times 10=1540000\mathrm{kg}$

The centre of mass of the water, according to the centre of mass idea, is located (20 + 5) h from the top.
Work done = mg(20+5)

$work done=150000\times 10\times 25=385MJ$

Hence the correct answer is 385MJ.