Fermi Questions Marathon

[danny9696]

"How many atoms of Helium are in the average classroom?"

A classroom is about 3x10x10 = 300 meters cubed = 3E8 cm^3
Liter = cm^3 = 3E8 liters
PV = nRT, assume P and R to be 1: 3E8 = 3E2K (n)
n=1E6 moles of all gases
Helium is BARELY present in air, probably something parts per million so 1E6/1E6 = 1 mol of helium
6E23 atoms, therefore around 24 <- fermi answer

Question: How long would it take for light from Alpha Centauri to reach the Earth in minutes?

[hmcginny]

Speed of light is 3E8 m/s, distance to alpha tauri is probably E12 meters (just a guess, but its probably within 1 or 2), so it would take .33E4 or 3E3 seconds, which is 5E1 minutes, which is on the border, but I'll assume alpha tauri is on the lower end of E12 meters so lets go with E1 minutes.

How many hairs are on a typical house cat?

[AlphaTauri]

Eh, I'd have to disagree there, hmcginny. Alpha Centauri is about 4.3 light years from Earth, so it'd take the light 4.3 years to reach us - which converts to 4.3 years * 365.25 days * 24 hours * 60 minutes = 2.3E6 minutes.

Or the short way - E0 years * E2 days/year * E1 hours/day * E2 minutes/hour = E5, which is pretty close (not sure where/if I should round up to make it E6, as I don't do Fermi).

[hmcginny]

well looks like my estimate was way off, if i had started with the right number (E17 meters) I would have gotten it. whoops. question still stands about how many hairs there are on a typical house cat though.

[aditya8081]

Lets estimate that a standard housecat is a cylinder of radius 10 cm and a length of 30 cm.
This means that the Surface area of a house cat is about 2*pi*10 cm* 30cm + 2*pi* (10 cm)^2, which comes out to 60 cm^2 + 600 cm^2, so Surface Area= 7e2 cm^2 The average follicle density of a cat is about 10 hairs / sq cm, so 7e3 hairs, meaning my answer will be 4

Now my Fermi Question:
If all of cornfields in the US were used to make popcorn for one year, how massive would the resulting popcorn be?

[JTMess]

US produces 1.3E10 bushels of corn per year. 50 ears in bushel = 6.5E11 ears per year. Estimation that 10 ears make a m^3 of popcorn = 6.5E10 m^3 of popcorn, making the final answer 11.

Question: How tall are you (lightyears)?

[quizbowl]

US produces 1.3E10 bushels of corn per year. 50 ears in bushel = 6.5E11 ears per year. Estimation that 10 ears make a m^3 of popcorn = 6.5E10 m^3 of popcorn, making the final answer 11.

Question: How tall are you (lightyears)?

light travels 3E8 m/s, times 3E7 s/year we have 9E15 meters.
I'm just around 2E0 meters, so 2E0/9E15 = around E-16 light years.

If every person with the surname "Smith" in America brushed their teeth at the same time, how many gallons of water would be used during that time?

[OldSpice]

light travels 3E8 m/s, times 3E7 s/year we have 9E15 meters.
I'm just around 2E0 meters, so 2E0/9E15 = around E-16 light years.

If every person with the surname "Smith" in America brushed their teeth at the same time, how many gallons of water would be used during that time?

I'm going to say around 1 in 1000 people have the surname smith (maybe less)
so number of smiths in america is
E-3 * E8 = E5
E0 gallons per toothbrushing
E5 gallons

how many people are drinking coffee right now?

[cngu23]

light travels 3E8 m/s, times 3E7 s/year we have 9E15 meters.
I'm just around 2E0 meters, so 2E0/9E15 = around E-16 light years.

If every person with the surname "Smith" in America brushed their teeth at the same time, how many gallons of water would be used during that time?

I'm going to say around 1 in 1000 people have the surname smith (maybe less)
so number of smiths in america is
E-3 * E8 = E5
E0 gallons per toothbrushing
E5 gallons

how many people are drinking coffee right now?

approximately 7E9 people in the world
I'll saw around 2E9 of them are in night time zone/sleeping.
of those that are awake, 1 out of every 100 of them are drinking something.
1 of every 10 people drinking something are drinking coffee.
5E6 people are drinking coffee right now.

How many people in Europe own an iPad?

[r31415]

About 1E9 people in Europe
About 1/5 of them have iPads
=2E8

How many pencils can fit in a 10m x 10m x20m box?