We had learn to calculate nuclear energy in science school using E=mc2 equation and the answer in joules. but does it really make sense that the real energy level it emited? Albert Einstein write this equation just to amaze the people how intense the energy of the nuclear atomic particle can give out. He just simply put the equation as enormous as possible by using the speed of light because he just thinking the long number of speed of light it can given in meter length, then raise the power of 2 to make it even astounding.
If you really wanted to find the exact answer of energy in joule the atomic energy can give out, E=mc2 really cant give you the correct or exact answer, unlike 1+1=2 , E may not given by mc2. it all depends on particle quality, temperature, pressure, humidity level, source of origin, impurity content, ways of particle interaction with each other,proximity or distance of particle, speed of particles and so on.
needless to say more, Albert Einstein also can put E=mc3 or even mc4 as he like to indicate the powerful energy it emit, it just a symbolic, it doen't intended to give accurate energy level. If one really wanna to find the real energy the particles can give out, there must be a very long complicated equation that God knows.
So just forget it to put in the school text book to let the student calculate the energy level, it just waste of resource and make student more stupid. Just like we all have studied that our solar system have 9 planet and it proven wrong when Pluto is not a planet recently. the knowledge we acquired may not true, perhaps some more planet wil join in from outer space when its path stray within our solar system in distant future.
just tell you all frankly, even Albert Einstein don't use E=mc2 to calculate the atomic bomb energy in joules that bomb Japan... so how dare you all using that equation so seriously in school to calculate energy?