Physics Help Forum Continuity Equation

 Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

Dec 1st 2015, 10:44 AM   #1
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Join Date: Nov 2015
Posts: 3
Continuity Equation

I have attached a problem. I think the answer is v1=v2 because of the continuity equation A1*v1=A2*v2. Because it has a uniform cross section A1=A2 so v1=v2.

It seems like this problem gives a lot of extra information though. I don't need to use Bernoulli's equation for this correct?

Attached Files
 Physics Problem.pdf (63.7 KB, 12 views)

 Dec 1st 2015, 11:25 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 Remember that the "A" in your equation is the cross-section area of the fluid, which may not be the same as the cross-section of the pipe. Clearly the fluid picks up kinetic energy as it descends down the incline, so v2 > v1. Which means A2 < A1. Hence if the fluid entering the pipe completely fills the crosss-section of the pipe, then when it exits the fluid's cross-sectional area is less than the area of the pipe. Bottom line: yes, use Bernoulli.
 Feb 4th 2016, 11:45 AM #3 Junior Member   Join Date: Feb 2016 Posts: 16 continuity A1*V1=A2*V2 this is true for one dimensional case (v=v(x) but here you have v=v(x,y) and then continuity becomes du/dx+dv/dy=0 use the energy eqn (Bernoulli )

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