Question: At a certain location, the horizontal component of the earth's magnetic field is 4.6E-5 T, due north. A proton moves eastward with just the right speed, so the magnetic force on it balances the weight. Find the speed of the proton.
In equilibrium, weight of the proton (downward)=magnetic force(upward)
m*g = ...
This solution includes the equation needed to obtain the answer for calculating speed as it pertains to the concept of magnetism for this problem. The equation is gone through step-by-step, all the way to and including the final answer, in a very easy to follow manner.