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Help with Bernoulli's Equation

  • Thread starter mm874
  • Start date
  • #1
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Homework Statement



The gauge pressure in a horizontal fire hose of diameter 5.4 cm is 3.0 x 105 Nm-2 and the speed of flow is 4.0 ms-1. The fire hose ends in a metal tip of diameter 2.5 cm. What are the pressure and the speed of the water in the tip?

Homework Equations




P+ρgh+0.5ρv^2=Constant
Volumetric Flow rate = A*v
Mass Flow Rate = ρ*Volumetric Flow rate

The Attempt at a Solution



Volumetric Flow rate = 0.00229*4 = 0.00916m3/s
Speed at end of hose = 0.00916/0.000491 = 18.67m/s

300000 + (0.5*1000*4^2) = P2 + (0.5*1000*18.67)
= 308000 = P2+174845

∴ P2 = 308000-17845 = 133155Pascals or 1.3 Bar

I am just checking this is right. As this is the answer I keep getting but the tutorial answers show something different.
 

Answers and Replies

  • #2
Andrew Mason
Science Advisor
Homework Helper
7,603
354
You have to square the 18.67. Check your arithmetic. I get 133,716 N/m^2.

AM
 
Last edited:

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