Jump to content

# Question about e=mc2

## Recommended Posts

In the famous equation, how is c the velocity of light expressed?

How do you express velocity, without a refrence to distance or time?

##### Share on other sites

Short answer: C is invariant.

This basically means that the speed of light is the same in all reference frames.

##### Share on other sites

ok, But what is the number?

how do we express velocity?

C=~300000000m/s

##### Share on other sites

Thanks. The next question is, how do we express m (mass)

is it just in grams?

##### Share on other sites

velocity in meters per second and mass in kilograms gives you energy in joules.

##### Share on other sites

thank you very much

##### Share on other sites

Is this correct?

the amount of energy contained in 1kg of matter 1*(300000000*300000000)=90000000000000000joules.

##### Share on other sites

Yes. It would be nice to write 9x1016J though.

##### Share on other sites

it's not completely right...momentum...

##### Share on other sites

I think we can safely assume that the block is stationary in this case.

##### Share on other sites

stationary relative to what?

##### Share on other sites

$E^2=(mc^2)^2+({\rho}c)^2$

##### Share on other sites

Now how to tap to tap all that energy, oh the wonders..

##### Share on other sites

fission, fusion, matter/antimatter anhialation

##### Share on other sites

pogos just imagine that the block is in a universe all by its self and is stationary relative to the universe(assume its a universe where you canfind the centre easily)

##### Share on other sites

Is this correct?

the amount of energy contained in 1kg of matter 1*(300000000*300000000)=90000000000000000joules.

In nuclear weapons, only a very very tiny amount of the actual material used in the bomb is converted to energy. Im not sure of the exact figure but i think it was only a few grams.

##### Share on other sites

In nuclear weapons, only a very very tiny amount of the actual material used in the bomb is converted to energy. Im not sure of the exact figure but i think it was only a few grams.

I did some rough calculations and using estimates of energy yields, determined approximately the amount of mass that was converted into energy for both the Little Boy dropped on Hiroshima and the Fat Man dropped on Nagasaki.

The Little Boy was composed of uranium-235 and although the critical mass, or the mass needed to sustain a chain reaction, for U-235 is 50 kg, only approximately 0.6043 grams were converted to energy.

The Fat Man, made of plutonium-239, had a critical mass of only 10 kg yet only between 0.9297 and 1.162 grams of plutonium were actually converted to energy.

##### Share on other sites

Ah i remember now - that sounds about right.

That's not a lot of mass considering the size of the explosions :\

##### Share on other sites

Living in a world so advanced in technology and so overwhelmed with conflict makes those numbers seem even smaller.

An extension of the calculations above using rather conservative death toll estimates shows that on the average it took only 7.470 micrograms (10^-6 g) to kill a single person in Nagasaki and just 4.316 micrograms per individual with the more efficient uranium bomb dropped on Hiroshima. (To put it in perspective, each fragment of a paperclip cut into one million pieces would weigh one microgram.) One can only imagine what 60 years of scientific advancement has done to those figures.

##### Share on other sites

Living in a world so advanced in technology and so overwhelmed with conflict makes those numbers seem even smaller.

An extension of the calculations above using rather conservative death toll estimates shows that on the average it took only 7.470 micrograms (10^-6 g) to kill a single person in Nagasaki and just 4.316 micrograms per individual with the more efficient uranium bomb dropped on Hiroshima. (To put it in perspective' date=' each fragment of a paperclip cut into one million pieces would weigh one microgram.) One can only imagine what 60 years of scientific advancement has done to those figures.[/quote']

60 years of scientific advancement hasn't changed the speed of light...

##### Share on other sites

Lol i think he means the amount of mass used up in the explosions. It's efficiency i think.

##### Share on other sites

Lol i think he means the amount of mass used up in the explosions. It's efficiency i think.

The efficiency of how much energy you get from a set amount of mass is given by c2

OTOH, you could become more efficient by converting a higher fraction of the bomb's mass to energy, but those relevant numbers aren't the ones that were quoted, as far as I can tell.

##### Share on other sites

Naturally I meant that the mass converted into energy would be increased by 60 years of scientific advancement.

For example, I know that separating U-235 isotopes was a major challenge. 60 years of advancement would allow for more pure samples of U-235 to be separated, potentially making a more destructive bomb by increasing the amount of mass converted to energy.

Also, a bound on the size of the atomic bomb was the weight allowance of the airplane used to transport it. Today's larger bombers obviously have larger payloads and would be able carry approximately 3 times more weight than the Enola Gay. A bigger bomb would allow for more mass to be converted to energy, making the bomb deadlier still.

The point that I was trying to make is that there are many scenarios we can come up with that would allow for more mass to be converted to energy. I apologize for not being more explicit.

##### Share on other sites

You forgot to mention the ICBMs on Subs... each sub can hold up to 24 ballistic missiles with up to 10 warheads on each, with each warhead capable of leveling a city.

Did you know that if a SSBN was its own country, it would be the third largest nuclear power in the world? (after the US and Russia)

## Create an account or sign in to comment

You need to be a member in order to leave a comment

## Create an account

Sign up for a new account in our community. It's easy!

Register a new account

## Sign in

Already have an account? Sign in here.

Sign In Now
×

• #### Activity

• Leaderboard
×
• Create New...

## Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.