Question

A manometer connected to a closed tap reads $3.5\times {10}^{5}N/m^2$. When the valve is opened, the reading of manometer falls to $3.0\times {10}^{5}N/m^2,$ then velocity of flow of water is

• A. 100 m/s
• B. 10 m/s
• C. 1 m/s
• D.

Answer 1

The correct option is B 10 m/s

Bernoulli's theorem for unit mass of liquid $\frac{p}{\rho }+\frac{1}{2}{v}^2$ = constant
As the liquid starts flowing, it pressure energy decreases $\frac{1}{2}{v}^2=\frac{P_1-P_2}{\rho }\Rightarrow \frac{1}{2}{v}^2=\frac{3.5\times {10}^5-3\times {10}^5}{{10}^3}\Rightarrow v^2=\frac{2\times 0.5\times {10}^5}{{10}^3}\Rightarrow v^2=100\Rightarrow v=10m/s$