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Riddle with flowing water

  1. Oct 25, 2016 #1

    micromass

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    zzz.png

    Assume the water flows from the faucet sufficiently slow.
     
  2. jcsd
  3. Oct 25, 2016 #2

    Borg

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    3 and 4 at the same time.
     
  4. Oct 25, 2016 #3

    DaveC426913

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    To be perfectly pedantic, 3 will be full fractions of a second before 4, but yeah, 3 and 4.
     
  5. Oct 25, 2016 #4

    billy_joule

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    looks like 3 would be full before it starts overflowing into 4
     
  6. Oct 25, 2016 #5
    3

    These little puzzles are fun.. Tx micromass! :oldsmile:
     
  7. Oct 26, 2016 #6

    Borek

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    Depends on how you define "full". I am assuming it means "overflowing". Then, it is still a function of how fast water is added from the tap. Or, more precisely, it depends on whether the water is added faster than it can flow through the tubes connecting tanks.

    If it is added slow enough, 3 and 4 with overflow at almost the same time. If it is added pretty fast, it will overflow the first tank first.
     
  8. Oct 26, 2016 #7

    micromass

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    The speed of the water was specified in the OP.
     
  9. Oct 26, 2016 #8

    Borek

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    ROFL, completely missed the description below the image.
     
  10. Oct 26, 2016 #9
    Three?
    Four?
    Has got to be one of those 2
     
  11. Oct 26, 2016 #10

    Ygggdrasil

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    Four. Water pressure from tank #3 will make the level of tank 4 slightly higher than the level of tank 3.
     
  12. Oct 26, 2016 #11

    DaveC426913

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    I disagree. The only way there would be positive pressure from 3 into 4 (once they're at the same height) is if 3 is slightly more full. The water still has to get to 4 by going from high water level to low water level - even if it's one drop at a time. It ain't gonna flow uphill.

    And remember, it states the water is filling sufficiently slow.
     
  13. Oct 26, 2016 #12

    Ygggdrasil

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    Consider the force balance for water in the tube connecting tanks 3 and 4. If tanks 3 and 4 have the same height of water (above the inlet to tank 4), how much water is pushing on the outlet from tank 3? Is this more or less than the amount of water pushing on the inlet to tank 4?
     
  14. Oct 26, 2016 #13

    rbelli1

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    3 will fill first. As flow approaches zero the difference in time between the filling of 3 and 4 will approach zero.

    BoB
     
  15. Oct 26, 2016 #14

    rbelli1

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    There is actually more water pushing into tank 4. You have the volume of tank 2 as well. This is irrelevant.

    If you turn off the tap where you have tank 4 filled nearly to the top you have 3 filled to the same level. When you turn your tap on you need the level of tank 3 to rise slightly to cause a pressure imbalance in the pipe to have flow. Tank 3 will always have to be higher in order to fill 4 more.

    BoB
     
  16. Oct 26, 2016 #15

    DaveC426913

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    It's the same. Otherwise there would be flow.

    There can never be more water in 4 than in 3.

    At some point, when 3 and 4 are equal, a subsequent drop will enter 3, making it one drop higher. Only then will water flow from 3 to 4.

    See rebellis post, above.
     
  17. Oct 27, 2016 #16

    Ygggdrasil

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    Ok, on second thought, you and @rbelli1 are correct.
     
  18. Oct 27, 2016 #17

    Student100

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    Hard water forms a mineral deposit in the outlet from 1 to 2, thus, one is the answer.
     
  19. Oct 27, 2016 #18

    Borek

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    What about water in the tube? It pushes back as well, it is not just about tanks.
     
  20. Oct 28, 2016 #19

    Fervent Freyja

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    It looks as if 3 will fill a moment before 4. I don't see 2 being able to completely fill, as 3 is spilling water received from it. If that is the case, then 1 cannot be filled either.
     
  21. Oct 28, 2016 #20
    you were right the other time.¨
    Another word definition game problem.
    "sufficiently slow" sets a baseline for the flow, and direction to the baseline, and that can be set at any level for a desired result.

    Example:
    In your Lambougini travelling down the highway, a police car flashes and pulls you over.
    The policeman says that you were going sufficiently slow so as to acquire a speeding ticket.
    He explains that the speed limit is 65 mph, the car will do at least 300 mph, but you at 66 mph, were sufficiently slow to still register on radar.
    You were going slower than the maximum speed of the car but not slow enough.

    Most policemen use the same baseline, but the approach is from the bottom up - sufficiently slow is anything 65 mph and under.
    They would say you were driving sufficiently fast to warrant a ticket.

    So 1 can fill before 2,3, or 4.
     
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