
$A =0.4\, m ^{2}$
$a =1 \,cm ^{2}$
$H =40 \,cm$
Using Bernoulli's equation
$\Rightarrow\left( P _{0}+\frac{ mg }{ A }\right)+\rho gH + \frac{1}{2} \rho V _{1}^{2}$
$=P_{0}+0+\frac{1}{2} \rho v^{2}.....(1)$
$\Rightarrow$ Neglecting $v _{1}$
$\Rightarrow v =\sqrt{2 gH +\frac{2 mg }{ A \rho}}$
$\Rightarrow v =\sqrt{8+1.2}$
$\Rightarrow v =3.033\, m / s$
$\Rightarrow v \simeq 3 \,m / s$



( Atmospheric pressure = $76\ cm$ of $Hg$)