In the figure, a particle moves along a circle in a region of uniform magnetic field of magnitude B- 4.2 mT. The particle is either a proton or an electron (you must decide which). It experiences a magnetic force of magnitude 2.8 x 10 15 N. What are (a) the particle's speed, (b) the radius of the circle, and (c) the period of the motion? (a) Number (b) Number (e) Number Units Units Units ni_