Answer
$$
4.1 \mathrm{m} / \mathrm{s}
$$
Work Step by Step
We have $\Delta p=p_{1}=2.0$ atm. Consequently,
$$
v=\sqrt{\frac{2 \Delta p}{\rho\left((A / a)^{2}-1\right)}}=\sqrt{\frac{4\left(1.01 \times 10^{5} \mathrm{Pa}\right)}{\left(1000 \mathrm{kg} / \mathrm{m}^{3}\right)\left[(5 a / a)^{2}-1\right]}}=4.1 \mathrm{m} / \mathrm{s}
$$
