A pressure-pump has a horizontal tube of cross-sectional area $10 \mathrm{~cm}^2$ for the outflow of water at a speed of $20 \mathrm{~m} / \mathrm{s}$. The force exerted on the vertical wall just in front of the tube which stops water horizontally flowing out of the tube, is: [given : density of water $=1000 \mathrm{~kg} / \mathrm{m}^3$ ]