RAJASTHAN PMT Rajasthan - PMT Solved Paper-2007

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

    A)  10.3 m/s                             

    B)  2.8 m/s

    C)  5.6 m/s               

    D)         8.4 m/s

    Correct Answer: A

    Solution :

    Bernoullis equation for flowing liquid be written as                 \[p+\frac{1}{2}\rho {{v}^{2}}+pgh=\]constant    ... (i) Here,\[p=\]pressure energy per unit volume of liquid \[\rho =\]density of liquid (water) \[h=\]height of liquid column \[v=\]velocity of liquid and  \[g=\]acceleration due to gravity Dividing Eq. (i) by\[\rho g\], we have                 \[\frac{p}{\rho g}+\frac{{{v}^{2}}}{2g}+h=\]constant In this expression, \[\frac{{{v}^{2}}}{2g}\]is velocity head and\[\frac{p}{\rho g}\]is pressure head. It is given that,                 velocity head = pressure head \[ie,\]    \[\frac{{{v}^{2}}}{2g}=\frac{p}{\rho g}\] or            \[{{v}^{2}}=\frac{2p}{\rho }\] or            \[{{v}^{2}}=\frac{2\times 13.6\times {{10}^{3}}\times 40\times {{10}^{-2}}\times 9.8}{{{10}^{3}}}\]


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