# Homework Help: Relativistic nuclear energy

1. Sep 18, 2014

### leehufford

1. The problem statement, all variables and given/known data

In a nuclear reactor, each atom of uranium (235 amu) releases about 200 MeV when it fissions. What is the change in mass when 1.0 kg of uranium 235 is fissioned?

2. Relevant equations

E = mc2

3. The attempt at a solution

I found the energy released per kg based on the numbers above, plugged it in to the above formula and got a number I do not think is reasonable: 9.11 x 10-10. That number reminds me of the mass of an electron, only its orders of magnitude higher. Am I oversimplifying this problem? It really has me confused. Thanks in advance,

Lee

Last edited: Sep 18, 2014
2. Sep 18, 2014

### cwasdqwe

Knowing the mass of each uranium atom we can compute the energy released (Joule in the IS of units) for each gram of uranium.
It is important to always have in mind the units we are using. You don't explicit the units you're using when you calculate energy, but the energy of 1 Kg of Uranium must be way higher than that...

I've found for you that 1kg of U235 (3,75%) has 83,14 TJ/kg :O