A simple pendulum with a bob of mass $m=1kg$, charge $q=5\mu C$ and string length $l=1m$ is given a horizontal velocity $u$ in a uniform electric field $E=2\times {10}^{6}V/m$ at its bottommost point $A$, as shown in figure. It is given that the speed $u$ is such that the particle leaves the circle at pint $C$. Find the speed $u$ (Take $g=10m/s^2$ )