
Physics: What does it take to put a waterfall on a skyscraper? - haser_au
https://www.wired.com/story/what-does-it-take-to-put-a-waterfall-on-a-skyscraper/
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haser_au
Homework questions from the article (feel free to offer corrections):

Q: Estimate how much it would cost to run this for a day (pick a price for
electricity in dollars per kilowatt * hr).

Usage: 3.39 million Watts

Cost of electricity in Australia: $0.25 per kWh

Cost per hour: $847.50

Q: If the water fell with no air resistance, how fast would it be traveling
when it hit the ground?

Height: 108 metres

Gravity 9.8m^2 m/s

velocity = sqrt(2 * gravity * distance) = sqrt(2 * 9.8 * 108) = 46 m/s

Q: Suppose you want to make this waterfall be human powered. How many humans
would need to pump water if each human can maintain a power output of 50
Watts?

Usage: 3.39 million Watts

Human Output: 50 Watts

Humans required: 67,800

Q: Suppose you want to make this thing solar powered and only run while the
sun is shinning. How big of a solar panel would you need? Assume the solar
panel produces 500 Watts per square meter.

Usage: 3.39 million Watts

Solar Panel output: 500 Watts/square metre

Size required: 6,780 square metres (1.26 NFL football fields, 1/3rd of the MCG
in Melbourne)

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Someone
Firstly, the building is in China, so Australian electricity pricing doesn’t
matter :-)

Also, from the article: _”That 's fine, but that's wrong. According to this
site, the waterfall has a power requirement of 185 kWatts.”_

⇒ your estimates are off by a factor of about 18. It’s (ballpark) $50, 3500,
350 m².

However, that _”this site”_ talks about _”four 185-kilowatt pumps”_
([https://www.scottishconstructionnow.com/27846/and-
finally-35...](https://www.scottishconstructionnow.com/27846/and-
finally-350ft-tall-artificial-waterfall-added-to-outside-of-chinese-
skyscraper/#)) ⇒ assuming all four pumps are fully active all the time,
multiply the above by 4.

Finally, from the same page:

 _”The electricity bill for just one hour of operation is a whopping 800 yuan
(£89), he added.

“That’s why we don’t switch on the waterfall every day – only for special
festivities in the city,” he said.”_

