An Electron Moves in a Region Where the Magnetic Field

Multiple Choice

An electron moves in a region where the magnetic field is uniform and has a magnitude of 80 μT. The electron follows a helical path which has a pitch of 9.0 mm and a radius of 2.0 mm. What is the speed of this electron as it moves in this region?

A) 48 km/s
B) 28 km/s
C) 20 km/s
D) 35 km/s
E) 8.0 km/s