A city built its water supply system with hollow metal pipes that are as uniformly thin as having only two inches (roughly 5 cm) of outer diameter at any point. However the pipe-built system is able to deliver water at a rate of more than 10 tons per second at a single section, or even more. How is it possible?

Note: The answer is practical, so you cannot assume that water goes as fast as 1000 m/s in the pipe, or having hundreds of pipes going together at one place (a few pipes together is a common practice, but not too many), or anything else impossible in real life.

  • $\begingroup$ Which part of the accepted answer is the correct one? $\endgroup$ – Rubio Apr 9 at 4:09
  • $\begingroup$ @Rubio The top part is the expected answer. $\endgroup$ – iBug Apr 9 at 4:28
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    $\begingroup$ Your definition of "practical" and mine apparently differ. :) $\endgroup$ – Rubio Apr 9 at 5:58
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    $\begingroup$ @Rubio The other way: I forgot to mention that the pipe is the only tool in the delivery system. $\endgroup$ – iBug Apr 9 at 8:16

It seems to me that there are at least two ways.

First, just because you built your system with hollow pipes doesn't mean you need to use them as pipes. Take lots of the pipes, arrange them in a ring, solder or weld them together along their length, and then send the water down the middle.


second, the question doesn't say 10 tons per second per pipe. So maybe they just have lots and lots and lots of pipes, and 10 tons/second is the total delivery.

Hmm, a third possibility:

"that are as thin as having only two inches of diameter" could mean that 2" is the smallest diameter of any of the pipes but some might be much larger. So maybe there are ickle tiny 2" pipes that don't deliver much water, and enormous 10' ones that deliver a very great deal.


The water is

pumped through the pipes into water trucks, and delivered to the destination in bulk.

Or perhaps

There are dozens or hundreds of pipes involved, which in aggregate can deliver the total volume mentioned without overtaxing any individual pipe. Not really practical, but the question doesn't actually say (currently anyway) that the system is able to deliver over 10 tons of water per second through a single 2" diameter pipe.

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    $\begingroup$ Ha. Your second answer is the same as my second answer ... but I got there several seconds before you did :-). $\endgroup$ – Gareth McCaughan Apr 8 at 18:13

I think it happens because:

When you said : "hollow metal pipes that are as thin as having only two inches", you did not say "hollow metal pipe". That means there might be multiple pipes in the system. That must be a big city for so many pipes!


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