Answer
$\boxed{v=\sqrt {\frac{2\rho g h}{\rho_{air}}}}$
Work Step by Step
Applying the Bernoulli’s equation between the points $B$ and $A$, we obtain
$P_B+\frac{1}{2}\rho_{air}v_B^2+\rho_{air}gh=P_A+\frac{1}{2}\rho_{air}v_A^2+\rho_{air}gh$
or, $P_B+\frac{1}{2}\rho_{air}v^2=P_A+\frac{1}{2}\rho_{air}0^2$
or, $\frac{1}{2}\rho_{air}v^2=P_A-P_B$
or, or, $\frac{1}{2}\rho_{air}v^2=\rho g h$
or, $\boxed{v=\sqrt {\frac{2\rho g h}{\rho_{air}}}}$
