Question

What is the kinetic energy of an electron in electron volts with mass equal to double its rest mass?

Answer 1

If m₀ is the rest mass of an electron and c is the speed of light, then kinetic energy (E) of the electron = mc² − m₀c². ...(1)

According to the question,
m = 2m₀

E = (2m₀ − m₀)c²
E= m₀c² = 9.1 × 10⁻³¹ × 9 × 10¹⁶ J

$E=\frac{9.1\times 9}{1.6}\times \frac{{10}^{-15}}{{10}^{-19}}=51.18\times {10}^4\mathrm{eV}=511\mathrm{keV}$