Relativistic Kinetic Energy?

Question

I saw that the Relativistic Kinetic Energy calculation for these two sources, seems to be different :

http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

see : Conservation of Energy

EK = gamma*m*c^2

While here :

http://en.wikipedia.org/wiki/Kinetic_energy

see : Relativistic kinetic energy of rigid bodies

EK = gamma*m*c^2 - m*c^2

Which one is right ? Or did I misunderstand something ?

Answer 1

Hi,

the right equation is the second one. Infact Kinetic Energy is equal to total energy (gamma*m*c^2)- rest energy (m*c^2) of the body. So the first equation is the expression of total energy and not of the kinetic energy. In the first site there's not mention of kinetic energy.That's ok? Bye!

Answer 2

You have misread the Wiki equation and the equation does not appear on the other site (ucr.edu)...

...unless I missed something...

Answer 3

They are talking about different things.  The first link you posted are talking about calculating the amount of fuel (antimatter/matter in this case) needed to travel between two places using the conservation of energy.  The rocket is at rest at the starting point and the destination.  The second link you posted is for calculating the atual kinetic energy that the rocket posses while in motion.  Completely different things.

Answer 4

Why do you hurt people's brains with these kind of questions? lol