A positively charged bead (point-like charge q) moves with 710 frictions along a vertical rod, as sketched in Fig., subject both to the Earth gravity and to the electric force due to another positive point-like charge Q fixed at the lower end of the cod. The bead is observed to execute an oscillating motion between "levels" A and B shown in the figure along with the relevant geometrical dimensions. Based on this observation, find mass m of the bead. The bead and fixed charge have small sizes that can be neglected in comparison with other dimensions.
