A charged cork ball of mass $m$ is suspended on a light string in the presence of a uniform electric field, as shown in Figure P23.53. When $\mathbf{E}=(A \mathbf{i}+B \mathbf{j}) \mathrm{N} / \mathrm{C}$, where $A$ and $B$ are positive numbers, the ball is in equilibrium at the angle $\theta$. Find (a) the charge on the ball and (b) the tension in the string.