Let A = cross-section of tank

a = cross-section hole

V = velocity with which level decreases

v = velocity of efflux

From equation of continuity $av = AV \Rightarrow v = \frac{av}{A}.$

By using Bernoulli's theorem for energy per unit volume

Energy per unit volume at point A

= Energy per unit volume at point B

$P + \rho gh + \frac{1}{2} \rho v^{2} = P + 0 + \frac{1}{2} \rho v^{2}$

⇒ ⇒ $v^{2} = \frac{2gh}{1-\left(\frac{a}{A}\right)^{2}} = \frac{2 \times 10 \times (3 - 0.525)}{1 - (0.1)^{2}} = 50 (m/sec)^{2}$