Question

show the advantages of developing of E=mc^2

Answer 1

It has advantage it shows that energy and mass are interconvertable

Answer 2

, for example.

The bit that you need to hear to get it is probably this:
You don't have intuition for what energy and mass are. All you know are: 'weight' is a thing (there are heavy and light things), 'heat' is a thing, and the equations you learned in intro physics class convinced you that a mystical numerical quantity called 'energy' is a thing.

 It's really easy, starting out, to think you know that energy is 'having motion' (which is what heat is, since molecules are moving around or vibrating very fast). But that breaks down when you look at photons - they all move the same speed; how can their energy vary? Then you learn that it's proportional to frequency and you amend your 'intuition' to include that.

When you get to special relativity it becomes apparent that, yes, velocities (and therefore energies) can change in difference reference frames, but so can masses. The math and experiments demonstrate that the energy of a particle when it isn't moving is E=mc2" role="presentation" style="margin: 0px; padding: 0px; outline: 0px; display: inline; font-style: normal; font-weight: normal; line-height: normal; font-size: 15px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">E=mc2E=mc2, which is required for energy/momentum conservation, among other things.

The more deep understanding comes when you realize that c2" role="presentation" style="margin: 0px; padding: 0px; outline: 0px; display: inline; font-style: normal; font-weight: normal; line-height: normal; font-size: 15px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">c2c2 is just a conversion factor, like converting between Celsius and Fahrenheit. It doesn't mean anything; we made it up. So the equation is really E=m" role="presentation" style="margin: 0px; padding: 0px; outline: 0px; display: inline; font-style: normal; font-weight: normal; line-height: normal; font-size: 15px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">E=mE=m. Don't read that as 'mass is equal to energy', read it as 'energy and mass are measuring the same thing'.

And note that for moving particles it's E=m+p" role="presentation" style="margin: 0px; padding: 0px; outline: 0px; display: inline; font-style: normal; font-weight: normal; line-height: normal; font-size: 15px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">E=m+pE=m+p, except for the conversion factors.