## Fermi Questions C

whythelongface
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### Re: Fermi Questions C

A Trident D5 has a significantly larger yield than one megaton TNT equivalent. If I remember properly, it should be able to destroy land on the scale of E4 square kilometers
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UTF-8 U+6211 U+662F
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### Re: Fermi Questions C

Question: If, in a distant galaxy, there is a direct linear correlation between number of humanoids and surface area of the inhabited planet, and the Earth just so happens to fit the model perfectly, what is the gravitational force between a planet with 10 trillion humanoids, and a humanoid on the surafce of the planet, that has a mass of 100 kg? Give your answer in newtons. Assume all habitable planets have the same density as the earth.
```Gravitational acceleration is 9.8 m/s^2 or around 1E1. There are around 8 billion people on Earth. 10 trillion / 8 billion is around 1E3 (if we're using the short system for trillion). Ratio of surface areas is around 1E3. Ratio of radii is around 3E1. Ratio of volumes is around 27E3 or 3E4. Ratio of masses is then around 3E4. 1E1*100*3E4/3E1=1E6. Fermi answer: 6.

Edit: Need to divide by 3E1 again. Fermi answer: 4```
`9.8 m/s^2 * sqrt(10 trillion humanoids/7.442 billion humanoids) * 100 kg = 3.6E4.`
How many drops of 0.1 M HCl would it take to turn Lake Victoria to a pH of 3?
Last edited by UTF-8 U+6211 U+662F on July 2nd, 2018, 7:32 pm, edited 3 times in total.

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### Re: Fermi Questions C

`Gravitational acceleration is 9.8 m/s^2 or around 1E1. There are around 8 billion people on Earth. 10 trillion / 8 billion is around 1E3 (if we're using the short system for trillion). Ratio of surface areas is around 1E3. Ratio of radii is around 3E1. Ratio of volumes is around 27E3 or 3E4. Ratio of masses is then around 3E4. 1E1*100*3E4/3E1=1E6. Fermi answer: 6.`
Radius is squared so 1E6 is divided by 3E1 again so final answer I think is 3E4 or 4
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UTF-8 U+6211 U+662F
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### Re: Fermi Questions C

`Gravitational acceleration is 9.8 m/s^2 or around 1E1. There are around 8 billion people on Earth. 10 trillion / 8 billion is around 1E3 (if we're using the short system for trillion). Ratio of surface areas is around 1E3. Ratio of radii is around 3E1. Ratio of volumes is around 27E3 or 3E4. Ratio of masses is then around 3E4. 1E1*100*3E4/3E1=1E6. Fermi answer: 6.`
Radius is squared so 1E6 is divided by 3E1 again so final answer I think is 3E4 or 4
Oh yeah, my bad (this does not bode well for my upcoming physics exam)

UTF-8 U+6211 U+662F
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### Re: Fermi Questions C

How many drops of 0.1 M HCl would it take to turn Lake Victoria to a pH of 3?
Just reminding everyone this is here.

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### Re: Fermi Questions C

How many drops of 0.1 M HCl would it take to turn Lake Victoria to a pH of 3?
Just reminding everyone this is here.
Revival time!
`Estimate lake victorias volume to be around eries so 4E2 cubic km or 4E14 liters. Im pretty sure that the current concentration doesn't matter. If one drop has .1 M of HCl 4E15 drops would give a pH of 1 (I think) and 4E13 for a pH of 3 so 13`
`the actual volume is 2750 cubic km which doesn't affect the final value. However Wikipedia says 1 mole / liter is a pH of 0 not 1 so final answer 12???`
Question: what is the density of the universe in kg/m cubed?
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