Proton 1 moves with a speed v from the east coast to the west coast in the continental United States; proton 2 moves with the same speed from the southern United States toward Canada.

(a) Is the magnitude of the magnetic force experienced by proton 2 greater than, less than, or equal to the force experienced by proton 1?

(b) Choose the best explanation from among the following:

I. The protons experience the same force because the magnetic field is the same and their speeds are the same.

II. Proton 1 experiences the greater force because it moves at right angles to the magnetic field.

III. Proton 2 experiences the greater force because it moves in the same direction as the magnetic field.