Question

Two particles $X$ and $Y$, of equal mass and with unequal positive charges, are free to move and are initially far away from each other. With $Y$ at rest, $X$ begins to move towards it with initial velocity $u$. After a long time, finally

• A. $X$ will stop, $Y$ will move with velocity $u$
• B. $X$ and $Y$ will both move with velocities $u/2$ each
• C. $X$ will stop, $Y$ will move with velocity < $u$
• D. both will move with velocities <$u/2$

Answer 1

The correct option is A $X$ will stop, $Y$ will move with velocity $u$

Initially both charges are far apart so there is no electrostatics force but when X starts moving then
Electrostatics force $F=\frac{k{q}_1{q}_2}{r^2}$
Given that both masses have positive charges, so they will repel each other.
Force on the X will be opposite to direction of displacement so it will stop after some time.
And Y starts moving as force is acting on it