Fermi Questions C

[Raleway]

Good try! The last answer would have received credit, and I'm pretty sure most wouldn't have gotten close e.e

How many years of sleep would the regular human need (avg based) to reach the total amount of time since the universe was created?

[Adi1008]

Good try! The last answer would have received credit, and I'm pretty sure most wouldn't have gotten close e.e

How many years of sleep would the regular human need (avg based) to reach the total amount of time since the universe was created?

My attempt (Click to Show Hidden Text)

Assume one person sleeps 8 hours a day. There's 24 hours in a day, so it's 1/3 of the time. In three years, a person sleeps one year's worth of time.
The universe is 13.7 billion years old, or 1.37 E10 years. Three times that is 4.11E10, giving a Fermi Answer of 10

Actual answer (Click to Show Hidden Text)

[url=http://www.gallup.com/poll/166553/less-recommended-amount-sleep.aspx]This[/url] says that Americans get about 6.8 hours of sleep. That's one year of sleep every 3.53 years. Doing 3.53*1.37 E10 gives a Fermi Answer of 10 (although just barely)

How many US dollar bills would it take in order to create a stack from Mumbai to Istanbul?

[Unome]

Stacked flat I assume? (Click to Show Hidden Text)

- Guesstimating the distance is around 2.5E6 meters
- Stacks of dollar bills - probably similar to paper, so 4E1 per centimeter = 4E3 per meter.
- Multiply to get ~E10
Fermi Answer: 10

True Answer (Click to Show Hidden Text)

- A single dollar bill is .0043 inches, which is ~9155 per meter
- Using [url=http://www.gcmap.com/]this tool[/url], the distance is 2997 miles = ~4823204 meters
- Multiply to get 4.4E10 - a good example of two bad estimates canceling out :P 
True Answer: 10

How many pieces of letter paper would it take to cover a single C60 carbon fullerene?

[appleshake123]

Guess (Click to Show Hidden Text)

I know from some lab in chem a few years back that iron had an atomic radius of 125 pm. Carbon is higher to the right, so it is less, but by not to much, so carbon has an atomic radius of e-10 m. Surface area of a sphere b/c fullerene 4*pi*r^2, so surface area is 12(e-10)^2 = e-19m^2. Letter paper is 8.5"x11" or about 100in^2 *(6,25ish cm^2)* e-4 m^2  or about e-1 m^2. So to cover c60 carbon fullerene, you need e-18 letter paper. FA = -18

Internet answer (Click to Show Hidden Text)

DIameter of fulleren is 7A or 7e-10, so Radius of 3.5e-10.. Surface area is 1.5 E-18. Letter paper is 6*e-2 m^2. You need about 2.5 E-17 of paper so FA = -17.
I underestimated the surface area by not adjusting for the radius.

With fans blowing at a flat wooden board on the back of a skateboard, how many desktop fans is needed to propel the average man lying on the skateboard on a tennis court?

[talkingturtle101]

Bringing this thread back.

My Answer (Click to Show Hidden Text)

- It would maybe take 500 J of energy to lift a person 1 foot off the ground.
- A fan from a desktop could maybe provides 0.1 J, so Fermi Answer of 3

Actual Answer (Click to Show Hidden Text)

- It takes 1.36 J to lift one pound one foot off the ground. So if a person weighs 150 pounds, this is about 200 J.
- I couldn't find how much energy a desk fan could provide, but it might be 1 J, so Fermi Answer of 2?
- Sorry for the really terrible answer.

[Unome]

Bringing this thread back.

My Answer (Click to Show Hidden Text)

- It would maybe take 500 J of energy to lift a person 1 foot off the ground.
- A fan from a desktop could maybe provides 0.1 J, so Fermi Answer of 3

Actual Answer (Click to Show Hidden Text)

- It takes 1.36 J to lift one pound one foot off the ground. So if a person weighs 150 pounds, this is about 200 J.
- I couldn't find how much energy a desk fan could provide, but it might be 1 J, so Fermi Answer of 2?
- Sorry for the really terrible answer.

Btw we need a question to answer

[Magikarpmaster629]

Hey, would any of you be interested in a question marathon live for Fermi Questions? We did one for Fast Facts way back in like October (I'll find the link when I'm not on mobile) and I'd like to get a second one going (really should have done this earlier...)

[NeilMehta]

Hey, would any of you be interested in a question marathon live for Fermi Questions? We did one for Fast Facts way back in like October (I'll find the link when I'm not on mobile) and I'd like to get a second one going (really should have done this earlier...)

I would love to join, but maybe later in the summer once all of us have wrapped up finals

[talkingturtle101]

Btw we need a question to answer

Whoops I forgot. During the time it takes Tchaikovsky's 1812 Overture to play, how many times could light go from the Earth to the moon?

[Unome]

Nice one (Click to Show Hidden Text)

- Estimated time it takes, 3 minutes, ~2E2 seconds (idk wild guess, maybe it's more because classical + why else would you mention it in a Fermi question?)
- Light takes ~5E2 seconds to go to the sun and back, I'd estimate less than a hundredth as far to the moon (probably a lot closer actually, idk.), so ~5E-1 seconds
- Therefore, E3
Fermi Answer: 3

True Answer (Click to Show Hidden Text)

Tchaikovsky's 1812 Overture is 900 seconds long
- The moon is 384,400 km away so it takes light around 1.2813 seconds for the round-trip
- Dividing the two gives 702.41 seconds.
Fermi Answer: 3

What was the average rate of text messages sent, in messages per second, during 2016?