The Lorentz force law is
$\begin{align*}\mathbf{F} = q \left(\mathbf{E} + \mathbf{v} \times \mathbf{B} \right)\end{align*}$
Initially, $\mathbf{v} = 0$ , so the second term inside the parenthesis is $\mathbf{0}$ . So, at $t = 0$ , the particle experiences a force in the direction of the electric field, which gives the particle a velocity in the direction of the electric field. Since $\mathbf{v}$ and $\mathbf{B}$ are parallel, the second term inside the parenthesis is still $\mathbf{0}$ . So, the particle will continue to move in a straight line and not experience any magnetic force. Therefore, answer (E) is correct.

Solution to 1986 Problem 25