Bernoulli’s law?

1. The problem statement, all variables and given/known data
What gauge pressure in the water mains is necessary if a fire hose is to spray water to a height of 25 m?

2. Relevant equations
Bernoulli’s equation(?)

3. 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.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

http://ift.tt/1dglOLK

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