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Homework Help: Why would adding more water increase the velocity of the water?

  1. Aug 7, 2014 #1
    1. The problem statement, all variables and given/known data

    Students must create an irrigation system that takes water from a reservoir 80 cm deep to a wave pool across the room. A perfectly leveled horizontal tube with constant circumference takes water from the bottom of the reservoir to the wave pool.

    Why would adding more water results in a grater velocity of the water as it exits the tube? The solutions book states that the velocity of the water as it leaves the reservoir is only related to the depth of water in the reservoir which I understand. But adding more water doesn't increase the depth of the water right?

    So why would adding more water increase the velocity of the water as it exits the tube to enter the wave pool?
  2. jcsd
  3. Aug 7, 2014 #2


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    Gold Member

    How does adding water NOT change the depth? If you have a cube (for simplicity) and you have some water in it, it has some volume of water equal to l*w*h. If I come along with a hose and start dumping water into it, what's going to happen?
  4. Aug 7, 2014 #3
    But the hole from which the water leaves the reservoir is fixed, so that depth doesn't change right?
  5. Aug 7, 2014 #4


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    Staff: Mentor

    If by "adding more water" you mean that the reservoir width and/or length is increased accordingly so that the water level remains fixed then yes, the exit velocity will remain the same. On the other hand, if it means adding more water to a fixed geometry reservoir then the water depth must increase. Otherwise, where will the extra water be stored?
  6. Aug 7, 2014 #5
    Oh shoot I keep mixing up depth with H. Depth is the distance from the surface of the resevoir to the point in the resevoir not from the ground to the point. So if more water is added then D will increase which will result in a greater efflux speed! It makes sense now. Thank you both for your help!
  7. Aug 7, 2014 #6


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    Gold Member

    no problemo broseph
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