In a high-energy collision between a cosmic-ray particle and a
particle near the top of Earth's atmosphere, 104 km above sea
level, a pion is created.The pion has a total energy E of 1.92 ×
105 MeV and is traveling vertically downward. In the
pion's rest frame, the pion decays 35.0 ns after its creation. At
what altitude above sea level, as measured from Earth's reference
frame, does the decay occur? The rest energy of a pion is 139.6
MeV.