Halliday, Resnick & Walker — Magnetic Fields: Problem 50

50 A proton travels through uniform magnetic and electric fields. The magnetic field is \(\vec{B} = -3.25\hat{i} \text{ mT}\). At one instant the velocity of the proton is \(\vec{v} = 2000\hat{j} \text{ m/s}\). At that instant and in unit-vector notation, what is the net force acting on the proton if the electric field is (a) \(4.00\hat{k} \text{ V/m}\), (b) \(-4.00\hat{k} \text{ V/m}\), and (c) \(4.00\hat{i} \text{ V/m}\)?