試題詳解

19. A certain elementary particle has a mass that is 207 times that of an electron. That type of particle has a proper lifetime of 2.20×10^-6 s. What is the particle's kinetic energy (MeV) if we measure its lifetime as 8.17×10^-6s? The electron's rest energy is 0.511 MeV.
(A) 2.87×10²,
(B) 1.24×10³,
(C) 6.33×10⁴,
(D) 9.87×10²,
(E) 1.54×10⁴.