Special Relativity - Relativistic Energy

A free electron (rest mass m_e = 0.5 MeV/c²) has a total energy of 1.5 MeV. Its momentum p in units of MeV/c is about

A. 0.86
B. 1.0
C. 1.4
D. 1.5
E. 2.0

(GR9277 #85)

Solution:

E² = p²c² + m₀²c⁴

1.5² = p²c² + (0.5/c²)²c⁴

 p²c² = 1.5² − 0.5² = 2

p = ^√2/_c ≈ ^1.4/_c

Answer: C