Question

As the speed of a particle increases, its rest mass

• A. increases
• B. decreases
• C. remains the same
• D. changes

Answer 1

Answer: (C)

remains the same

Rest mass $\left(m_o\right)$ is defined as the mass of the object at rest (or in rest frame) which remains constant.

Only the mass of the moving object changes as the speed increases via $m=\frac{m_o}{\sqrt{1-\frac{v^2}{c^2}}}$

Hence option C is correct.