$A$ charged particle $q$ is shot towards another charged particle $Q$ which is fixed,with a speed $v$. It approaches $Q$ up to a closest distance $r$ and then returns. If $q$ were given a speed $2v$,the closest distance of approach would be

An electron moving with a speed of $5 \times 10^6 \, m/s$ is shot parallel to an electric field of intensity $1 \times 10^3 \, N/C$. The field causes retardation of the electron's motion. Evaluate the distance traveled by the electron before coming to rest for an instant (mass of $e = 9 \times 10^{-31} \, kg$,charge $q = 1.6 \times 10^{-19} \, C$).

$A$ small point mass carrying some positive charge is released from the edge of a table. There is a uniform electric field in this region in the horizontal direction. Which of the following options correctly describes the trajectory of the mass? (Curves are drawn schematically and are not to scale).

An electron and a positron enter a uniform electric field $E$ perpendicular to it with equal speeds at the same time. The distance of separation between them in the direction of the field after a time $t$ is (where $\frac{e}{m}$ is the specific charge of the electron).

$A$ hot filament liberates an electron with zero initial velocity. The anode potential is $1200 \,V$. The speed of the electron when it strikes the anode is

In Millikan's experiment,an oil drop having charge $q$ becomes stationary upon applying a potential difference $V$ between two plates separated by a distance $d$. The weight of the drop is