$A$ point charge $2 \times 10^{-2} \, C$ is moved from $P$ to $S$ in a uniform electric field of $30 \, N C^{-1}$ directed along the positive $x$-axis. If the coordinates of $P$ and $S$ are $(1, 2, 0) \, m$ and $(0, 0, 0) \, m$ respectively,the work done by the electric field will be $......... \, mJ$.

Consider a spherical shell of radius $R$ with a total charge $+Q$ uniformly spread on its surface (centre of the shell lies at the origin $x=0$). Two point charges $+q$ and $-q$ are brought,one after the other,from far away and placed at $x=-a/2$ and $x=+a/2$ $(a < 2R)$,respectively. The magnitude of the work done in this process is:

$A$ particle $A$ has charge $+q$ and a particle $B$ has charge $+4q$,with each of them having the same mass $m$. When allowed to fall from rest through the same electric potential difference,the ratio of their speeds $\frac{v_A}{v_B}$ will be:

Two charges $7 \ \mu C$ and $-2 \ \mu C$ are placed at $(-9, 0, 0) \ cm$ and $(9, 0, 0) \ cm$ respectively in an external field $E = \frac{A}{r^2} \hat{r}$, where $A = 9 \times 10^5 \ N/C \cdot m^2$. Considering the potential at infinity is $0$, the electrostatic energy of the configuration is . . . . . . $J$.

Two point charges $100\,\mu C$ and $5\,\mu C$ are placed at points $A$ and $B$ respectively,with $AB = 40\,cm$. Calculate the work done by an external force in displacing the charge $5\,\mu C$ from $B$ to $C$,where $BC = 30\,cm$ and $\angle ABC = \frac{\pi}{2}$. Given $\frac{1}{4\pi\varepsilon_0} = 9 \times 10^9\,N m^2/C^2$.

$A$ ball of mass $1 \, g$ and charge $10^{-8} \, C$ moves from point $A$ $(V_A = 600 \, V)$ to point $B$ where the potential is zero. The velocity of the ball at point $B$ is $20 \, cm/s$. Find the velocity of the ball at point $A$ in $cm/s$.