- #1

bigplanet401

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## Homework Statement

What gauge pressure in the water mains is necessary if a fire hose is to spray water to a height of 25 m?

## Homework Equations

Bernoulli's equation(?)

## The Attempt at a Solution

I tried figuring out what water velocity was needed to make the water spray up 25 meters. The expression I got (using conservation of energy) was

[tex]

v_0 = \sqrt{2 g h}

[/tex]

But then I get confused and try to argue that, by Bernoulli's law,

[tex]

P_G + \frac{1}{2} \rho v^2 + 0 = 0 + 0 + \rho g h

[/tex]

and so the gauge pressure should be zero (using the expression above for the velocity). Thanks for any help.