Question

A horizontal jet of water coming out of a pipe of area of cross-section $20c{m}^2$ hits a vertical wall with a velocity of $10m{s}^{-1}$ and rebounds with the same speed. The force exerted by water on the wall is:

• A. $0.2N$
• B. $10N$
• C. $400N$
• D. $200N$

Answer 1

The correct option is C $400N$

Volume of water coming out of the pipe per sec = A$\times v=20\times {10}^{-4}\times 10=0.02m^3/s$

mass of water hitting the wall per sec = m = $0.02\times {10}^3=20$ kg/sec

force=$\frac{2mv}{t}$=$2\times 20\times 10=400N$