Velocity of water out of reservoir.

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Discussion Overview

The discussion revolves around determining the efflux speed of water from a cylindrical tank, specifically exploring the relationship between the speed and the depth of the water. Participants are considering both theoretical and practical approaches to derive the constant in the equation relating efflux speed to water depth.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes that the efflux speed is proportional to the square root of the depth of the hole, expressed as u = k sqrt(w), and seeks assistance in determining the constant k.
  • Another participant suggests that if viscous effects are ignored, the efflux speed can be derived from the balance of dynamic and static pressures, leading to the conclusion that v = sqrt(2g*h), thus indicating that the constant k is sqrt(2g).
  • A different participant challenges the necessity of considering pressure in the calculations, stating it is not part of their coursework.
  • Another participant emphasizes the need for both volume and pressure to accurately determine velocity in fluid dynamics, implying that additional factors may be required for a complete analysis.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of pressure in the calculations, with some supporting its inclusion and others arguing against it. The discussion remains unresolved regarding the best approach to determine the constant k.

Contextual Notes

There are limitations regarding the assumptions made about viscous effects and the applicability of pressure considerations based on participants' coursework. The discussion does not resolve the mathematical steps necessary to derive the constant k.

John09
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I have a cylindrical tank and I know that the efflux speed is proportional to the square root of the depth of the hole from the surface. So u=k sqrt(w). I need to algebraically determine the constant or k in that situation. Has anyone got any ideas as to how I should approach this? I was thinking that I could try and find the acceleration in i and j components and integrate it for velocity but didn't get far.

Thanks for any help.
 
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If you're ignoring the viscous effects, the efflux speed will be such that the dynamic pressure is equal to the static pressure just inside the hole. Dynamic pressure is 1/2*rho*v2, so rearranging for v, we can get that v = sqrt(2*p/rho). Since the pressure in a tank is simply from hydrostatic equilibrium (P = rho*g*h), we can plug in for P:

v = sqrt(2*rho*g*h/rho) = sqrt(2*g*h).

So, your constant is sqrt(2g).
 
Hm I don't think taking pressure into account is necessary as it is not part of our coursework.
 
If you want to know the velocity in fluid dynamics you need to know 2 things. Volume and pressure to find velocity. Unless you can invent some kinda new math cjl is right.
 

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