Two free point charges $+q$ and $+4q$ are a distance $R$ apart. $A$ third charge is so placed that the entire system is in equilibrium. Then the third charge is :-

One moving electron when comes closer to another stationary electron,then its kinetic energy and potential energy respectively . . . . . . and . . . . . . .

Two positively charged particles $X$ and $Y$ are initially far away from each other and at rest. $X$ begins to move towards $Y$ with some initial velocity. The total momentum and energy of the system are $p$ and $E$.

Two equal negative charges $-q$ are placed at points $(0, a)$ and $(0, -a)$ on the $Y$-axis. A positive charge $q$ is released from rest at point $(2a, 0)$. What will be the motion of this charge?

$A$ unit positive point charge of mass $m$ is projected with a velocity $V$ inside a tunnel as shown. The tunnel is made inside a uniformly charged non-conducting sphere of radius $R$ and volume charge density $\rho$. The minimum velocity with which the point charge should be projected such that it can reach the opposite end of the tunnel is equal to

Two point charges $4\,\mu C$ and $-1\,\mu C$ are kept at a distance of $3\ m$ from each other. What is the electric potential at the point where the electric field is zero?