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3

The equation is just the kinetic and rest energy, it does not include potential energy. But potential energy in relativity is not the proper concept. The linked question has some useful answers, but I think your true question is about how to learn to do things relativistically that you used to do non relativistically. And since the other answer so far takes ...

2

In classical mechanics there is no distinction between free and bound as far as this relation is concerned. In relativistic quantum mechanics (i.e. QFT), a particle that satisfies this relations is said to be "on-shell" or a physical observable asymptotically free particle. It is certainly not satisfied for virtual particles, but they are as their name ...

3

The mass of an atom is always less than the sum of the masses of the particles that compose it. The lack of mass (or energy, from E = mc^2) is called binding energy and it is the energy expended by the particles to remain confined inside of the atom. When fission occurs, not more spending of energy to hold together the individual particles. So the energy ...

18

A lot of different forms, but mostly kinetic energy. A good table is given at Hyperphysics. The energy released from fission of uranium-235 is about 215 MeV. This is divided into: Kinetic energy of fragments (heat): ~168 MeV Assorted gamma rays: ~15-24 MeV Beta particles (electrons/positrons) and their kinetic energy: ~8 MeV Assorted neutrons and their ...

3

The energy that is released when a the absorption of a neutron causes a heavy atom nucleus to fission into two daughter nuclei comes from the tighter binding energy of the two daughter nuclei compared to the weaker (smaller) binding energy of the original nucleus. This extra energy is mostly released in the form of the kinetic energy of the two daughter ...

1

A gold brick is made of gold atoms that mutually interact. At a given temperature it weighs bit less than the weight of each piece. At a higher temperature it weighs a bit more than at a colder temperature. So the weight isn't the sum of the weights of the parts, not quite. Even in a single gold atom, it weighs a little bit less than weight of each neutron ...

16

The problem is that the two calculations have hardly anything to do with one another - so it's no wonder you don't get the same result. The electron volt, as you say, measures the work you need to move an electron across a potential difference of one volt. On the other hand, if you want to calculate the mass of an electron using $E=mc^2$, what you need is ...

0

In the modern way of viewing things, no, (rest) mass is invariant. What happens is that the energy content of the body changes and some people still interpret this as a change in mass (which is an old point of view that, unfortunately, is fairly common). A nice discussion about this can be found here: ...

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