What's wrong with my calculation?

[scilover89]

"If a particle which has mass travel at the speed of light, the particle mass will reach infinity, which require infinity energy to move it, thus particle can't travel beyond the speed of light."
I made an calculation about it.(And it turned out to be wrong) However, I couldn't find the mistake!
This is my calculation:
Let the mass = 1kg, and the velotion = c
Kinetic energy gained while travelling=0.5mc^2
=0.5c^2
When these energy is fully converted into mass,
Einstein's Equation:E=mc^2
0.5c^2=mc^2
m=0.5
The mass gained by the particle is 0.5, not infinity? Why?

[vsage]

Simply put, you can't use classic formulae to describe the properties of matter at relativistic speeds. Use the relativistic formula for kinetic energy and you'll get a different answer detailed at http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/releng.html#c1 (near the bottom) where the m they use is not 1kg but can be calculated from http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html (near the bottom)

[russ_watters]

That equation describes the amount of energy released when turning mass into energy - it has nothing to do with relativistic mass.

[marlon]

and besides m = 1kg is nonsense because you are confusing rest-mass and relativistic mass. Keep in mind that mass is always interpreted as rest-mass though the epitheton rest is left behind...

marlon