Question

If a proton of mass m is moving with the velocity of light, its mass will be ________.

• A. unchanged
• B. large but finite
• C. infinite
• D. zero

Answer 1

The correct option is C infinite

Mass of a moving object $m = \dfrac{m_o}{0}{\sqrt{1-v^2/c^2}}$

where $m_o$ is the rest mass.

So, $v=c$

We get $m=\frac{m_o}{0}=\infty$.

So, mass of proton becomes infinite.