# Mv^2 or 1/2mv^2

combining wavelength(&)=h/mv and e=hv/& , we get e=mv^2
but kinetic energy is 1/2mv^2. where is other half?

## Answers and Replies

Hootenanny
Staff Emeritus
Science Advisor
Gold Member
combining wavelength(&)=h/mv and e=hv/& , we get e=mv^2
but kinetic energy is 1/2mv^2. where is other half?
Kinetic energy only takes the form 1/2mv2 in classical mechanics, which is only valid for low velocities. The full expression for relativistic kinetic energy is

$$T = mc^2\left(\gamma-1\right)$$

You should also note that your first two expression are only valid for v = c.

Fredrik
Staff Emeritus
Science Advisor
Gold Member
You might want to start with formulas that are actually correct, and not confuse relativistic stuff with non-relativistic stuff. Can you explain more clearly what formulas you're using and where you got them from? If you need greek symbols and don't know LaTeX, copy and paste from Redbelly98's https://www.physicsforums.com/blog.php?b=347 [Broken].

Last edited by a moderator:
THANKS, Hootenanny