A particle of mass 7.7 × 10-8 kg and charge +11 μC is traveling due east. It enters perpendicularly a magnetic field whose magnitude is 4.2 T. After entering the field, the particle completes one-half of a circle and exits the field traveling due west. How much time does the particle spend in the magnetic field?

1 answer

The force from the magnetic field equals centripetal force
Bqv=mv^2/r

v=Bqr/m

but PI*r/T=V so
PI*r/T=Bqr/m
Time=PI*m/Bq

check that.