Physics Help

SoSolid · 25 May 2006 at 10:29

I am stuck on this question can anyone help me with it please?

If the radius of the planet Krypton is one tenth of that of earth, what is the ration of their masses. How am I supposed to do this when no other information is supplied?

:confused:

decmatt · 25 May 2006 at 10:31

Depends, do they have the same relation in what materials are on the planet?

Socaddict · 25 May 2006 at 10:34

if thats all you have, assume they have the same densities. in which case mass will be proportional to volume, and hence you want the ratio of their volumes, which will be 4/3*pi*r^3

in which case the ratio of their volumes will be k*r^3 (k is a constant), so if the radius is 1/10th, then the ratio of volumes will be 1:1000.

That what you wanted?

SourChipmunk · 25 May 2006 at 10:37

It's a trick question. Krypton was made of a much denser material than the earth, creating a gravitational force 10 times greater than that of the Earth. That's where Superman gets his strength - generations of development on a 10G planet, ya get to Earth and everything weighs peanuts comparitively.

*note: don't quote me on the 10G thing. It might be more.

squiffy · 25 May 2006 at 10:41

Raist said:
It's a trick question. Krypton was made of a much denser material than the earth, creating a gravitational force 10 times greater than that of the Earth. That's where Superman gets his strength - generations of development on a 10G planet, ya get to Earth and everything weighs peanuts comparitively.

*note: don't quote me on the 10G thing. It might be more.

even a mountain?

Mellownatts · 25 May 2006 at 10:47

squiffy said:
even a mountain?

Compared to a mountain on Krypton, Yes.

Blackstar_solar · 25 May 2006 at 12:33

erm...is that a REAL question or did you make it up?

squiffy · 25 May 2006 at 12:37

Mellownatts said:
Compared to a mountain on Krypton, Yes.

yeah I know that, but it's unlikely a person born on a planet with 10x the mass will be able to pickup a mountain.

Blackstar_solar · 25 May 2006 at 12:40

they wouldn't be able to pick up a mountain on krypton, but (should/would) be able to on earth

daz · 25 May 2006 at 12:41

Superman gets his power from the Earth's yellow sun, Krypton's solar system had a red sun.

SoSolid · 25 May 2006 at 20:13

Socaddict said:
if thats all you have, assume they have the same densities. in which case mass will be proportional to volume, and hence you want the ratio of their volumes, which will be 4/3*pi*r^3

in which case the ratio of their volumes will be k*r^3 (k is a constant), so if the radius is 1/10th, then the ratio of volumes will be 1:1000.

That what you wanted?

Thanks for your help mate, have u basically just substitued the 1/10 into the formula for the volume of a sphere then?

Socaddict · 25 May 2006 at 21:02

basically, as its just the ratio of volumes, which is dependent on radius, assuming identical density.

Psyk · 25 May 2006 at 21:10

Pretty sure kryptonite is denser than anything you find on earth. They really should know their comic books before asking questions like this.

daz said:
Superman gets his power from the Earth's yellow sun, Krypton's solar system had a red sun.

I've never understood that. So they don't have powers on krypton? So when they are (were) at home they were pretty much the same as humans? How could a species evolve like that?

daz · 25 May 2006 at 21:23

Psyk said:
I've never understood that. So they don't have powers on krypton? So when they are (were) at home they were pretty much the same as humans? How could a species evolve like that?

Yeah they're apparently just normal like humans when they're at home.

God knows how it all works.

iCraig · 25 May 2006 at 21:25

Ask McDaniel, he used to live on Krypton.