Here is a question, I discovered 2 approaches to resolve it, differing in the answers and also I"m not sure why a method is incorrect.

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Question: A fire hose of cross area area A is compelled to direct a jet of water to a height h, the minimum power of the pump necessary for this hose is?

Method 1: $$ dp = ho A dxV$$$$ F = ho A V^2$$$$ P = F.V = ho A V^3$$

Method 2: $$ m = ho A dx$$$$ KE = frac12mV^2 = frac12 ho A dx V^2$$$$ P = frac12 ho A V^3$$

The correct answer stated is the one derived from method 2.Can anyone define why the initially strategy is wrong?

Thanks for your time.

homework-and-exercises energy-conservation work-related power
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asked May 18 "14 at 6:38

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Your initially strategy is wrong, bereason the velocity is not consistent in the time of the totality trajectory. This is what you implicitly assumed in the last step of the first method.

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answered May 18 "14 at 6:40

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