\(A =0.4\, m ^{2}\)

\(a =1 \,cm ^{2}\)

\(H =40 \,cm\)

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 \(v _{1}\)

\(\Rightarrow v =\sqrt{2 gH +\frac{2 mg }{ A \rho}}\)

\(\Rightarrow v =\sqrt{8+1.2}\)

\(\Rightarrow v =3.033\, m / s\)

\(\Rightarrow v \simeq 3 \,m / s\)