New value of the particle's total energy?

[vrobins1]

Homework Statement

A charged particle is observed to have a total energy of 0.642 MeV when it is moving at 0.700c. If this particle enters a linear accelerator and its speed is increased to 0.980c, what is the new value of the particle's total energy?

Homework Equations

Rest mass energy:
E₀=mc²

Kinetic energy:
K=($$\gamma$$-1)mc²

Total energy:
E=E₀+K

The Attempt at a Solution

I tried to solve for the rest mass energy using the original speed and total energy, but got stuck. I also tried to set up a ratio of old total E on top of new total E, but that didn't give me the correct answer.

Can anyone help? Thanks!

 

[LowlyPion]

Wouldn't you want to consider:

E = mc²/(1-v²/c²)^1/2

http://en.wikipedia.org/wiki/Mass_in_special_relativity#The_relativistic_energy-momentum_equation