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