A neutral particle is at rest in a uniform magnetic field B . At time t=0 , it decays into two charged particles, each of mass m .
a. If the charge of one of the particles is +q , what is the charge of the other?
b. The two particles move off in separate paths, both of them lie in the plane perpendicular to B . At a later time, the particles collide. Express the time from decay until collision in terms of m , B and q .