Water tower pressure question.

[catzzz88]

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A water tower is 40 meters tall. What is the highest building that the water tower can supply water to?

a) 50 m
b) 40 m
c) 30 m
d) 20 m

 

[MedPR]

A water tower is 40 meters tall. What is the highest building that the water tower can supply water to?

a) 50 m
b) 40 m
c) 30 m
d) 20 m

At max height the velocity of the fluid will be 0 and the pressure will be 0.

Plug those into bernoulli and you get h=Patm/rho*g

h=10.

A?

 

[chiddler]

energy is conserved. at the lowest point of the water tower, water is under some pressure. in order to reach 0 pressure, it must travel upwards 40 m so that gauge pressure becomes zero.

answer i think is 40.

to illustrate more mathematically:

P = rho*g*h
P = 10^3 * g * 40 = 4*10^5

this is how much pressure water is under at base of water tower.

how high can it go?

P = rho * g * h
4*10^5 = 10^3 * g * h

same numbers. h = 40.

 

[catzzz88]

I guessed B - 40 meters

yeah but I was getting all confused... the height at the TOP of the water tower is 40 m, but a building's height is measured by the top of the roof. So, if a building needs water and the building is 40 m high, the water only needs to get to ~ 35 meters to be considered supplying water to a 40 m building.... considering that the typical floor is roughly 5 meters in height....

am I overthinking this?

 

[MedPR]

I guessed B - 40 meters

yeah but I was getting all confused... the height at the TOP of the water tower is 40 m, but a building's height is measured by the top of the roof. So, if a building needs water and the building is 40 m high, the water only needs to get to ~ 35 meters to be considered supplying water to a 40 m building.... considering that the typical floor is roughly 5 meters in height....

am I overthinking this?

So the answer is 40? 🙁

 

[chiddler]

I guessed B - 40 meters

yeah but I was getting all confused... the height at the TOP of the water tower is 40 m, but a building's height is measured by the top of the roof. So, if a building needs water and the building is 40 m high, the water only needs to get to ~ 35 meters to be considered supplying water to a 40 m building.... considering that the typical floor is roughly 5 meters in height....

am I overthinking this?

i don't understand what you're trying to say

 

[milski]

Should be B) - if the pressure is supplied by the water tower, the same height will correspond to the same pressure. At 40 m the pressure of the water will be the same as the top of the tower, 1 atm, so the water will not flow anymore.

MedPR - you can't do much with Bernoulli here, at least in the way that you're using it. You cannot plug arbitrary numbers in it - there has to be some flow to use, so v should not be 0, the pressure at the top is 1 atm, not 0, and the whole left side equals a constant, which you don't know.

catzzz88, yes, I'd say you are overthinking it. 😉 Although if the building is 40 m, the faucets will be slightly below and everything will still work, while for 50 m building, faucets at 49 m won't work. So the answer stays the same even when overthought.

 

[milski]

i don't understand what you're trying to say

If the top of the roof of the building is at 40 m, the faucets will be somewhat lower, at say 37-39 m.

Btw, 5 m high floors would be nice and spacious. The reality is usually around half of that.

 

[chiddler]

If the top of the roof of the building is at 40 m, the faucets will be somewhat lower, at say 37-39 m.

Btw, 5 m high floors would be nice and spacious. The reality is usually around half of that.

lol

physics. where everything is perfect circle, a perfect vacuum, frictionless surface, and you can move a skateboard by placing a flashlight on top of it.

also there is a faucet on the apex of a building.

 

[milski]

lol

physics. where everything is perfect circle, a perfect vacuum, frictionless surface, and you can move a skateboard by placing a flashlight on top of it.

also there is a faucet on the apex of a building.

You mean like this:

Or like this:

 

[chiddler]

lol!

the second one is especially amazing!

 

[MedPR]

You mean like this:

Or like this:

Applicable to gen chem as well 👍

 

[MTHFR]

You mean like this:

Or like this:

This made my day.