$${v_0 = \sqrt{\frac{2 g h A_0}{A_0^2 - A^2}} \\ = \mathrm{\sqrt{\frac{(2)(9,8\, m/s^2)(0,045\, m)(0,35\, cm^2)}{(1,2\, cm^2)^2 (0,35\, cm^2)^2}}}\\ = 0,286\, \mathrm{m/s} = 28,6\, \mathrm{m/s}}$$