The mass of an electron at rest is `9.1 xx10^(-31)` kg. The energy of electron when it moves with speed of `1.8xx10^(8)` m/s is

Options

A. `2xx10^(-13)J`
B. `1xx10^(13)J`
C. `1.29xx10^(-13)J`
D. `1xx10^(-3) J`

Answer

C

Explanation

`m=m_(0)/sqrt(1-(v/c)^(2))=(9.1xx10^(-31))/sqrt(1-((1.8xx10^(8))/(3xx10^(8)))^(2))`
`=(9.1xx10^(-31))/sqrt(0.4)=(9.1xx10^(-31))/0.6324`
`m=14.38xx10^(-31)` kg
Now `E=mc^(2)`
`=14.38xx10^(-31)xx9xx10^(16)`
`=129.4xx10^(-15)`
`=1.294xx10^(-13)J`