When a negative charge is taken at a height from earth's surface, then its potential energy

The ratio of momenta of an electron and an $\alpha$-particle which are accelerated from rest by a potential difference of $100\, volts$ is

In space of horizontal $EF$ ($E = (mg)/q$) exist as shown in figure and a mass $m$ attached at the end of a light rod. If mass $m$ is released from the position shown in figure find the angular velocity of the rod when it passes through the bottom most position

A particle of mass $100\, gm$ and charge $2\, \mu C$ is released from a distance of $50\, cm$  from a fixed charge of $5\, \mu C$. Find the speed of the particle when its distance  from the  fixed charge becomes $3\, m$. Neglect any other force........$m/s$

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 $x=+a / 2( < R)$, respectively. Magnitude of the work done in this process is 

${\rm{ }}1\,ne\,V{\rm{ }} = {\rm{ }}......\,J.$ (Fill in the gap)