Question

Why mass changes in high speed?

Answer 1

This is as per theory of special relativity .

mass = m0 / [ 1 - u^2 / c^2 ]
m0 = rest mass.
u & c are speeds of a body & light respectively.

As per the formula if u > 0, m > m0.

If an object moves it has kinetic energy in addition to energy due to its mass. KE / c^2 adds to mass.

So mass increases.

According to E = m c^2 formula and other mechanics equations, we derive the equation.