Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Velocity of water out of reservoir.

  1. Aug 12, 2011 #1
    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.
  2. jcsd
  3. Aug 12, 2011 #2


    User Avatar

    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).
  4. Aug 12, 2011 #3
    Hm I don't think taking pressure into account is necessary as it is not part of our coursework.
  5. Aug 14, 2011 #4
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook