another magnetic freild question can soemone help me

[kevinlikesphysics]

A proton moves eastward in the plane of Earth's magnetic equator so that its distance from the ground remains constant. What is the speed of the proton if Earth's magnetic field points north and has a magnitude of 5.0 10-5 T?

[DaMastaofFisix]

It's all a matter of recognizing the forces at play. obviously, magnetic forces produce the net force, which is centriptal by nature. the Fc=FB, so using the given values for the B-field, the mass and charge of the proton, give it a shot.