A circle of radius $R$ is drawn with charge $+ q$ at the centre. A charge $q_0$ is brought from point $B$ to $C$, then work done is

A proton of mass $m$ and charge $e$ is projected from a very large distance towards an $\alpha$-particle with velocity $v$. Initially $\alpha$-particle is at rest, but it is free to move. If gravity is neglected, then the minimum separation along the straight line of their motion will be

A block of mass $m$ moving with speed $v$ compresses a spring through distance $x$ before its speed is halved. What is the value of spring constant ?

Three point charges $q, q$ and $-2 q$ are placed at the corners of an equilateral triangle of side '$L$'. Calculate work done by extemal force in moving all the charges far apart without acceleration

Potential atapoint $A$ is $3 $ $ volt$ and atapoint $B$ is $7$ $volt$,an electron is moving towards $A$ from $B.$

Two charged particles of masses $m$ and $2m$ have charges $+2q$ and $+q$ respectively. They are kept in uniform electric field and allowed to move for some time. The ratio of their kinetic energies will be