Question

An electron with (rest mass $m_0$) moves with a speed of $0.8c.$ Its mass when it moves with this speed is

• A. $m_0$
• B. $m_0/6$
• C. $5m_0/3$
• D. $3m_0/5$

Answer 1

The correct option is C $5m_0/3$

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