A vessel of area of cross-section A has liquid to a height H. There is a hole at the bottom of vessel having area of cross-section a. The time taken to decrease the level from H₁ to H₂ will be 

• A

  $\frac{\mathrm{A}}{\mathrm{a}}\sqrt{\frac{2}{\mathrm{g}}}[\sqrt{{\mathrm{H}}_1}-\sqrt{{\mathrm{H}}_2}]$

• B

  $\sqrt{2\mathrm{gh}}$

• C

  $\sqrt{2\mathrm{gh}({\mathrm{H}}_1-{\mathrm{H}}_2)}$

• D

  $\frac{\mathrm{A}}{\mathrm{a}}\sqrt{\frac{\mathrm{g}}{2}}[\sqrt{{\mathrm{H}}_1}-\sqrt{{\mathrm{H}}_2}]$