Kinetic energy, special relativity

[fluidistic]

Homework Statement

Calculate the kinetic energy of an electron whose momentum is 2MeV/c.

Homework Equations

P=\gamma m_0 v =mv.
E_K=(m-m_0)c^2.

The Attempt at a Solution

I'm told that \gamma m_0 v=\frac{2MeV}{c}.
If only I had the mass at rest of the electron (it isn't given in the problem), I could calculate its velocity with the first formula I gave. Then I could calculate its mass (not its rest mass, its apparent mass or whatever it's called). And then I could apply the third formula and this would solve the problem. Am I right?
So, should I look for the electron's rest mass in some book? Is there a missing data, or can I solve the problem without this info?

 

[aq1q]

You can do that. But you shouldn't have to look anything up. Do you know the relationship between \lambda (the lorentz factor) and v? if so, solve for the rest mass. Similarly, you can find the relationship between m and m_0. I hope that helps!

 

[fluidistic]

You can do that. But you shouldn't have to look anything up. Do you know the relationship between \lambda (the lorentz factor) and v? if so, solve for the rest mass. Similarly, you can find the relationship between m and m_0. I hope that helps!

I appreciate very much your help.
What I know is \gamma =\frac{1}{\sqrt {1-\frac{v^2}{c^2}}}. I don't know how to solve for the rest mass since v is unknown. I get m_0=\frac{P}{v}\sqrt {1-\frac{v^2}{c^2}} where P and c are known but not v...

 

[aq1q]

ahh what was i thinking. you're right! you need to look up the rest mass. I'm really sorry, at a quick glance I thought this was just algebra.

 

[fluidistic]

ahh what was i thinking. you're right! you need to look up the rest mass. I'm really sorry, at a quick glance I thought this was just algebra.

Ok thanks for your help. Problem solved!

 

[aq1q]

Ok thanks for your help. Problem solved!

great!