Question

At what speed, the velocity head of water is equal to pressure head of $40cm$ of Hg?

• A. $10.3m/s$
• B. $2.8m/s$
• C. $5.6m/s$
• D. $8.4m/s$

Answer 1

Answer: (A)

According to Bernouilli’s theorem
$P+\frac{1}{2}\rho v^2+\rho gh$ = constant
or, $\frac{P}{\rho g}+\frac{1}{2}\frac{v^2}{g}+h$ =constant
Velocity head $=v^2/2g$, pressure head $=P/\rho g$
Given $\frac{v^2}{2g}=\frac{P}{\rho g}$
$\therefore v^2=\frac{2P}{\rho }$
$\therefore V^2=\frac{2\times 13.6\times 10^3\times 40\times 10^{-2}\times 9.8}{10^3}$
or, $V=10.32m{s}^{-1}$