Question

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, $(g=10m{s}^{-2})$.

Answer 1

Total mass of water $=m$

$m=$ density $\times$volume

$=1000\times \pi R^2\left(h\right)$

$=1000\times \frac{22}{7}\times 7^2\times 10$

$=1540000kg$

By using center of mass concept ,center of mass of water is at depth of (20+5)h from the top.

Hence work done $=mg(20+5)$

$=150000\times 10\times 25$

$=385000000J$

$=385000KJ$