Question

What types of energy create a situation where conservation of energy cannot be used nicely?

please explain answer

Answer 1

In relativistic case mass and energy can change to one another, hence the presence of rest mass energy creates a situation where only conservation of energy is not applicable.

In relativistic cases, energy and mass both taken together are conserved not merely only energy or only mass. As according to special theory of relativity mass and energy can convert to one another, obeying famous einsteins mass energy equivalence relation E = mc^2 . Hence the presence of rest mass energy in matter restricts the conservation of energy only in relativistic cases.