Question

what you mean by energy conservation of mass

Answer 1

it means energy cannot be created nor destroyed but energy can change one form to another form.
for example electrical energy electric energy goes into bulb and bulb glows produces light energy and again light energy change for the forms.

Answer 2

Answer:Albert Einstein introduced his famous equation E = mc2 in a 1905 journal submission titled, "On the Electrodynamics of Moving Bodies." The paper presented his theory of special relativity, based on two postulates:

◆ Principle of Relativity: The laws of physics are the same for all inertial reference frames.

◆ Principle of Constancy of the Speed of Light: Light always propagates through a vacuum at a definite velocity, which is independent of the state of motion of the emitting body.

The first principle simply says that the laws of physics apply equally to everyone in all situations. The second principle is the more important one. It stipulates that the speed of light in a vacuum is constant. Unlike all other forms of motion, it is not measured differently for observers in different inertial frames of reference.

Explanation: