a
$ \text { Change in pressure }=\frac{1}{2} \rho \mathrm{v}^2 $
$ 4.5 \times 10^4-2.0 \times 10^4=\frac{1}{2} \times 10^3 \times \mathrm{v}^2 $
$ 2.5 \times 10^4=\frac{1}{2} \times 10^3 \times \mathrm{v}^2 $
$ \mathrm{v}^2=50 $
$ \mathrm{v}=\sqrt{50} $
$ \text { Velocity of water }=\sqrt{\mathrm{V}}=\sqrt{50} $
$ =\mathrm{V}=50$