Consider the free body diagram of the ball as shown below.
The expression of the net effective force on the ball is, Feff=Fe−Fg mgeff=mg−qE Substitute values, (10−3)geff=(10−3)(10)−(20×10−6)(100) geff=8×10−3N The minimum horizontal velocity that must be given to the ball at the lowest position can be calculated as, v=√5geffr v=√5(8)(