A proton, of mass 1.67×10 ^−²⁷ kg, moves in a circle in the plane perpendicular to a uniform magnetic field of magnitude 1.8 T. The radius of curvature is 3.0 cm. What is the speed of the proton?
a. 2.5 x 10⁵ m/s
b. 5.0 x 10⁵ m/s
c. 7.5 x 10⁵ m/s
d. 1.0 x 10⁶ m/s