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## Homework Statement

In a color television tube, electrons are accelerated through a potential difference of 20 000 volts. With what speed do the electrons strike the screen?

mass of electron=9.109*10^-31kg or 0.51099 MeV/c^2

## Homework Equations

I don't know which formula I have to use. When I use E=mc^2/sqrt(1-v^2/c^2) I first have to add the kinetic energy (20 000eV) and the rest energy of the electron (0.51099MeV) and than solve for x (which is v^2/c^2). The solution should be 0.27c but I never get it...Thank you!