Question

An electron has a rest mass of 9.11x10^-31 kg moves with a speed of 0.8c . find its kinetic energy

Answer 1

rest mass energy is $mc^{2}$.

where m is rest mass of electron

kinetic energy due to movement will be given as,

$\frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}} -mc^{2}$.

we know v = 0.8c

by putting values,KE = $5.466* 10^{-14}$ J

Answer 2

rest mass of electron , m₀ = 9.11 × 10⁻³¹ Kg

speed of electron , v = 0.8c

we know, total energy = mc² = m₈c²/(1 - v²/c²)

T.E = (9.11 × 10⁻³¹)*(3 * 10⁸)²/(1-0.64) = 9.11 * 10⁻¹⁵ * 9/0.36

T.E = 22.775 * 10⁻¹⁴ J

now, Kinetic energy = 22.775 * 10⁻¹⁴ - m₉c²

= 22.775 * 10⁻¹⁴ - 9.11 * 10⁻³¹ (3* 10⁸)²

= 14.576 * 10⁻¹⁴ J