The mass flow rate is given by the product of density (ρ), cross-sectional area (A), and velocity (v). The area of the circular pipe end is A = πr².

First, convert the radius to meters: r = 1.5 cm = 0.015 m.

Calculate the area: $\mathrm{A}={\mathrm{\pi r}}^2=\mathrm{\pi }\times {(0.015)}^2\approx 7.0686\times {10}^{-4}{\text{m}}^2$

Now, calculate the mass flow rate:

$\frac{\mathrm{dm}}{\mathrm{dt}}=\mathrm{\rho Av}=\left(1000\right)\times (7.0686\times {10}^{-4})\times (7.0)\approx 4.95\frac{\text{kg}}{\text{s}}$

This value is closest to 4.9 kg/s

Final Answer: 4.9kg/s