A muon is formed high in the Earth's atmosphere and travels at a speed 0.9 c with respect to the Earth. It travels for 20 km measured by Earth observer before decaying into other particles.
(a) How long does the muon exist as measured in the Earth's rest frame?
(b) What is the value of the Lorentz gamma factor associated with the muon's motion?
(c) How long does the muon exist as measured in the muon's rest frame?