Rotational KE vs Translational KE Q. Horizontal electric field E = mg/q exists as shown in the figure and a mass m is attached at the end of a light rod. if mass m is released from the position as shown in the figure. find the angular velocity at the bottom-most position
This is what my teacher did,But I don't see how is moving of bob accounting for rotational KE
 A: It is a rotation of a point mass about the pivot.
$I$ is the moment of inertia of the point mass about the pivot.
A: The ball has no translational kinetic energy. It has only rotational KE about the pivot. ($1/2I\omega^2$) . The work done by Electric field and gravity cause change in rot. KE. The rod has no rotational KE as it is assumed to be massless
A: $\let\om=\omega \def\half{{\textstyle {1 \over 2}}}$
I wish to argue against the harsh separation between translational and rotational KE I've read in a previous answer. From both conceptual and educational viewpoints.
To begin with, our system is very simple: a mass point constrained to move in a cicle. its velocity is obviously $v=\om\,l$ and its KE is 
$$\half m\,\om^2l^2.$$
There is no need to bring up the moment of inertia, which is a concept of mandatory use for complex systems, especially rigid ones. This IMHO holds for your teacher too.
But above all I object to @Tojrah statement

The ball has no translational kinetic energy. It has only rotational KE about the pivot.

Distinguishing between two kinds of KE may make sense for a system, where an important theorem by König holds:
Total KE of a system is the sum of KE of com $\rm G$, endowed with the total system mass, and KE of motion around com, where each point of system has velocity $\vec v - \vec v_{\rm G}$.
And also in this case the second term of König's theorem may be called "rotational KE" only if the system is rigid. Otherwise motion around com could be anything.
In any case KE of a system is defined beforehand as the sum of KE's of all its parts. Then König's theorem is shown. But when your system is a mass point there is no sense in speaking of translational vs. rotational KE: there is just one point, with one velocity and one KE: $\half mv^2$.
Edit A lapsus made me to credit Huygens for a theorem due to König almost a century later. I've corrected all references to that theorem.
