A muon (mass 106 MeV/c2) is produced in the upper atmosphere with an energy of 20000 MeV (20 GeV). In its rest frame, the muon decays 2.2 microseconds after it is produced. How far does the muon travel in the rest frame of the earth

Suppose a diode consists of a cylindrical cathode with a radius of 6.200×10^−2 cm , mounted coaxially within a cylindrical anode with a radius of 0.5580 cm . the potential difference between the anode and cathode is 260 v . an electron leaves the surface of the cathode with zero initial speed (v initial=0). find its speed vfinal when it strikes the anode.