What Is the Internal Energy of an Electron Moving at 0.750c0?

[Barry Melby]

Homework Statement

What is the internal energy of an electron moving at 0.750c0 in the Earth reference frame?

Homework Equations

The Attempt at a Solution

E = mc^2
E = (9.11 * 10^-31)(.750)(3*10^8)

However, this appears incorrect. What have I done wrong or what am i missing?

 

[DuckAmuck]

What do you mean "internal" energy? It's just one particle, so the options are "rest energy", "kinetic energy" and "total energy".
If m is the mass of an electron, c is light speed, and v is the speed of the electron, then:

Rest energy is E=mc^2
Total energy is E_T = \frac{mc^2}{ \sqrt{1 - \frac{v^2}{c^2}}}
Kinetic energy is KE = E_T - E

 

[mauveranger]

I ran into this post trying to solve a question from Pearson's Principles and Practices of Physics (by Mazur). The question is looking for the "intrinsic" energy: the energy of the particle when it appears at rest; i.e. $mc ^ 2$. I don't know why they use the wrong term or why they mention the speed of the particle.