What strength of magnetic field is used in a cyclotron in which protons make 3.5 x 10⁷ revolutions per second?

Calculate the maximum kinetic energy of the electron when a muon decays from rest via μ⁻ ⟶ e⁻ + vₑ + vμ. [Hint: In what direction do the two neutrinos move relative to the electron in order to give the electron the maximum kinetic energy? Both energy and momentum are conserved; use relativistic formulas.]

The mean lifetimes listed in Table 43–2 are in terms of proper time, measured in a reference frame where the particle is at rest. If a tau lepton is created with a kinetic energy of 920 MeV, how long would its track be as measured in the lab, on average, ignoring any collisions?