Back in the dawning heyday of the superhero, writers were still determining the extent of Superman's powers. There was a time when Superman's powers didn't come from our yellow sun. One important distinction between then and now was that Clark couldn't fly. He was only "able to leap tall buildings in a single bound". It was explained that his super strength was a result of Krypton's larger gravity.

So, Detective, based only on the statement that he is "able to leap tall buildings in a single bound", what was the mass of Krypton? Some help for this Fermi question: It's a good idea to guess that Krypton is about the same size as Earth. You might be interested in remembering some high school physics that to jump to a height (h) you initially need the same kinetic energy (KE = 0.5 * m*v^2) as the potential energy at the top of your jump (PE = m*g*h).

## 2009-06-24

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## 3 comments:

Guesstimation 1:

nt a superman follower, but i guess the "tall" bui;ldings he wld be jumping wld be arnd 50m?? or a gm of 10 and 100: 30?

now , running speed? i'll say 10m/s frm experience. (35kmph)

1/2 (10)^2= g*50 (or 30)

g= 1 or 1.5

kryptn's mass(m directly prprtnl to g) 10 or 7 times earth for same radius.

=> 6*(10)^25 or 3.5 * (10)^24

Guesstimation 2:

A sprinter jumps across hurdles appx 1m to 1.5m high.

So Mas of Krypton: 10/1 or 10/1.5

=> 10 or 7 times :)

Really great guesses. Nice and simple. That's what we're going for. But when I did this I said that a tall building was much bigger I said 100 stories with each story being about 9ft so a tall building being like 900ft. (Chrystler Building is 7 and the Empire State Building is 102)

To turn ft to m multiply by 0.3.

So something like 300m.

Good call using 50 instead of 30 to make the math easier. That's what it's all about.

My guess was 25 times the mass of earth (like I'll show in my post tomorrow) but 10 or 25. They are both the same magnitude. It's not like we're off by an order of magnitude. They're both good guesses. Good stuff.

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