Question

What is rest Mass? Why it should be necessary property of a charged body? Explain with detail

Answer 1

Rest mass of the body is defined as the inertial mass of the body when body is at rest.
Mass depends on the velocity of the body.
$$\begin{gathered} m=\frac{m_o}{\sqrt{1-{\displaystyle \frac{v^2}{c^2}}}} \\ where{m}_{o}istherestmass. \end{gathered}$$


Every charged body has protons and electrons , these are the particles with some rest mass.
therefore all charged body have rest mass.