**Momentum and energy is always conserved.**

p= γm_{o} v, where p is the relativistic momentum, v is the speed of the particle and m_{o} is its mass as measured by an observer at rest with respect to the particle.

Rest energy, E_{o} = m_{o}c^{2}

Total energy, E = γm_{o}c^{2}

Kinetic energy, KE = γm_{o}c^{2} – m_{o}c^{2}

∆E = ∆mc^{2}

E = γE_{o}

K.E = (γ – 1)E_{o}

E^{2} = p^{2}c^{2} + (m_{o}c^{2})^{2}**For particles that have zero mass, such as protons, m _{o} = 0, E = pc**

1 eV = 1.602 x 10^{-19} J

1 eV : energy required to accelerate an e- through a potential difference of 1 volt.

1 u = 1.66 x 10^{-27} J