The both of a pendulum has mass m = 1 kg and charge `q = 40mu C`. Length of pendulum is = 0.9 m. The point of suspensison also has the same charge `40 muC`. What is the minimum speed u (in m/s) should be imparted to the bob so that it can complete vertical circle ?

A ball of mass 1 g having a charge of 20 mu C is tied to one end of a string of length 0.9 m can rotate in a vertically plane in a uniform electric minimum horizontal velocity that must be given to the ball at the lowest position so that is complete the verticle circle is (let g= 10 ms^(-1))