Two balls each of mass $1 \mathrm{gm}$ are suspended by insulating strings each of $1 \mathrm{m}$. At equilibrium, angle between string and vertical is $30°$. Find charge on any one ball.

A particle is released from rest. in an electric field $\overrightarrow{\mathrm{E}}=5\mathrm{kV}/\mathrm{m} \hat{\mathrm{i}}$. Initially particle is at $\left(0,0\right)$. When displacement in $y$-direction is $84\mathrm{cm}$, then find displacement in $x$-direction.

[$g=9.8 \mathrm{m} {\mathrm{s}}^{-1}$ and $\frac{\mathrm{q}}{\mathrm{m}}=10\mathrm{\mu C}/\mathrm{kg}$

Three charges $-q_1,+q_2$ and $-q_3$ are placed as shown in the figure. The $x$-component of the force on $-q_1$ is proportional to: