Question
What is the kinetic energy in MeV of a $\pi$-meson that lives $1.40 \times 10^{-16} \textrm{ s}$ as measured in the laboratory, and $0.840 \times 10^{-16} \textrm{ s}$ when at rest relative to an observer, given that its rest energy is 135 MeV?
$90.0 \textrm{ MeV}$
Solution Video