One for the mathmaticians

51
Found 25th Sep 2017Edited by:"OllieSt"
It takes 5 minutes to fill a cylindrical water tank with a constant flow of water from the top

If you turn off the water flow and let the tank drain freely by gravitational force through a pipe on the bottom it takes 10 minutes to empty a fully filled tank.

How long will it take to fill the tank if the bottom pipe is left open?




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OllieSt2 m ago

Why?


because the floor would get very wet!
Banned
Diane Abbott has waded in with an answer, she said 45 minutes, no wait 34 seconds, no wait six firemen, no 12 ambulance drivers. She has had to phone Labour HQ for an answer, they will get back to her next week sometime.
51 Comments
25 Minutes
Not a mathematician - but would think 10 mins.

water flowing out is at half the rate of water coming in (5 mins to fill, 10 mins to empty) - hence net addition of water when you have both water flowing in as well as flowing out is exactly half of what you will have if you were only filling up (and not letting any outflow). Hence it should double the time from 5 mins to 10 mins
Answer is 10 minutes

That's 2 tanks filled up in 10 minutes, 1 tank emptied in 10 minutes leaving 1 full tank in 10 minutes..
Original Poster
The answer is not 10 minutes
Whilst a full tank discharges in ten minutes, the rate would not be constant, depending on the depth of liquid.
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42.

no what FP says
fivegoldstars3 m ago

Whilst a full tank discharges in ten minutes, the rate would not be …Whilst a full tank discharges in ten minutes, the rate would not be constant, depending on the depth of liquid.


Yes but that wouldn't make any difference
It would be the same filling as emptying
Edited by: "Wongy110" 25th Sep 2017
Wongy1104 m ago

Yes but that wouldn't make any difference It would be the same filling as …Yes but that wouldn't make any difference It would be the same filling as emptying



No, it would fill at a constant rate which would equate to a full tank at 5mins. However, if you let it fill with an open tap at the bottom, the discharge rate would vary depending on the depth of liquid.
time multiplied by space divided by pie add on the diameter of the sun minus earths gravity of course equals ...errrm... 7 & a half.

what prize have I won?
My initial thought was 20mins, now i can't remember how I even got to that!

please put me out of my misery and pm me the answer!
fivegoldstars8 m ago

No, it would fill at a constant rate which would equate to a full tank at …No, it would fill at a constant rate which would equate to a full tank at 5mins. However, if you let it fill with an open tap at the bottom, the discharge rate would vary depending on the depth of liquid.



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this is more a lesson of what not to do when you try to fill a tank, don't leave the blooming tap at the bottom open!
Original Poster
mutley147 s ago

this is more a lesson of what not to do when you try to fill a tank, don't …this is more a lesson of what not to do when you try to fill a tank, don't leave the blooming tap at the bottom open!


Why?
OllieSt2 m ago

Why?


because the floor would get very wet!
Original Poster
mutley11 m ago

because the floor would get very wet!



That much is true
A: Depends on what water level is in the tank when you start..
I'm going to assume this is a trick question somehow. Otherwise without getting overly complicated or reading the question like a riddle 10 minutes.
Original Poster
CoeK14 m ago

I'm going to assume this is a trick question somehow. Otherwise without …I'm going to assume this is a trick question somehow. Otherwise without getting overly complicated or reading the question like a riddle 10 minutes.


It's not a trick question.

Here's a starting point.


Let H be the fixed height of container, h be the current height of water,A be the cross-sectional area of the cylinder, and a be the cross-sectional area of the pipe at the bottom.

I think more info is required to give a definitive answer. Like dimensions or area.
master108 m ago

I think more info is required to give a definitive answer. Like …I think more info is required to give a definitive answer. Like dimensions or area.




It's three-dimensional and in Basingstoke.
Infinite as the top tap has been turned off "If you turn off the water flow".


What do I win?.
Edited by: ".MUFC." 25th Sep 2017
28.5 minutes.
Dark.Energy1 h, 6 m ago

time multiplied by space divided by pie add on the diameter of the sun …time multiplied by space divided by pie add on the diameter of the sun minus earths gravity of course equals ...errrm... 7 & a half. what prize have I won?


Mmmhhhh, pie.
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RossD8946 m ago

It's three-dimensional and in Basingstoke.

Do us a favour then and just run the trial on it. Simple.
OllieSt1 h, 11 m ago

It's not a trick question.Here's a starting point.Let H be the fixed …It's not a trick question.Here's a starting point.Let H be the fixed height of container, h be the current height of water, A be the cross-sectional area of the cylinder, and a be the cross-sectional area of the pipe at the bottom.



I'm an armchair mathematician at best, but I still don't think that this is enough to go off if you need the actual answer to the question. Fair enough if you're assuming constant rates in and out, but the output is subject to Toricelli's Law, so surely we need a numerical value for h to even begin?
Original Poster
You're a better man than I am, Gunga Din.


PM sent
The tank will never fill if you don't turn the tap on!
dougiegee20031 h, 13 m ago

The tank will never fill if you don't turn the tap on!


I think so. It depends if you think the word fill means actually turning the tap on also. If you gave some details about running speed etc and then said I ran from A to B and then stopped, how long would it take for me to run to C. You couldn't then say, I never said I started again from B. The fact that you have stated that you are going to be filling or running again means that water will be coming out of the tap and your legs will be moving. Or does it?
fivegoldstars1 h, 30 m ago

I'm an armchair mathematician at best, but I still don't think that this …I'm an armchair mathematician at best, but I still don't think that this is enough to go off if you need the actual answer to the question. Fair enough if you're assuming constant rates in and out, but the output is subject to Toricelli's Law, so surely we need a numerical value for h to even begin?


I was thinking bernoulli myself. But again don't think there is enough info to go on.
fivegoldstars1 h, 38 m ago

..... but the output is subject to Toricelli's Law, so surely we need a …..... but the output is subject to Toricelli's Law, so surely we need a numerical value for h to even begin?



CoeK7 m ago

I was thinking bernoulli myself. But again don't think there is enough …I was thinking bernoulli myself. But again don't think there is enough info to go on.



Surely you would just apply Vorderman theory?



MIDURIX19 m ago

I think so. It depends if you think the word fill means actually turning …I think so. It depends if you think the word fill means actually turning the tap on also. If you gave some details about running speed etc and then said I ran from A to B and then stopped, how long would it take for me to run to C. You couldn't then say, I never said I started again from B. The fact that you have stated that you are going to be filling or running again means that water will be coming out of the tap and your legs will be moving. Or does it?




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Original Poster
Here you go

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Yes that's correct, well done!
OllieSt27 m ago

Here you go[Image]


So "Infinite", I win lol.
Not very long.

Oh. So, if 'it would never fill up completely', how much water would be showing in the tank then? Would the level be at the top? Bottom? Middle?
Edited by: "deeky" 25th Sep 2017
Banned
Diane Abbott has waded in with an answer, she said 45 minutes, no wait 34 seconds, no wait six firemen, no 12 ambulance drivers. She has had to phone Labour HQ for an answer, they will get back to her next week sometime.
Graham197941 m ago

Diane Abbott has waded in with an answer, she said 45 minutes, no wait 34 …Diane Abbott has waded in with an answer, she said 45 minutes, no wait 34 seconds, no wait six firemen, no 12 ambulance drivers. She has had to phone Labour HQ for an answer, they will get back to her next week sometime.


Theresa May was going to give us the correct answer but just at the last minute decided it was not the right thing to do.

Kim Jong-un had the answer but strapped it to his other uncle who was strapped to a Hwasong-14 and just pressed the fire button meanwhile Trumps response was covfefe-((4X3-3'1627)/8)

Jeremy Corbyn is still trying to find the on button for his tablet.
Edited by: "philphil61" 25th Sep 2017
@OllieSt

"One for the mathmeticians"


Is this a trick question?
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