Question

An electron with (rest mass $m_0$ ) moves with a speed of $8.0c$. Its mass when it moves with this speed is

• A. $m_0$
• B. $\frac{m_0}{6}$
• C. $\frac{5m_0}{3}$
• D. $\frac{3m_0}{3}$

Answer 1

Answer: (C)

$m=\frac{m_0}{\sqrt{1-v^2/c^2}}$
$=\frac{m_0}{\sqrt{1-(0.8c{)}^2/c^2}}=\frac{5m_0}{3}$