Two small insulating spheres are attached to silk threads. The spheres have equal masses of `40 g` and have electric charges of `q_(1)=+2.0 muC` and `q_(2)=-2.0 mu C`. The spheres are brought into the initial positions shown in Figure(a), with a vertical separation of `15 cm` between them. In figure, the upper thread is slowly pulled upward, while point B is kept fixed. When point a has been raised through a height h, the lower sphere suddenly falls, as shown in Figure (b). The height h, is closest to:

Options

A. 9 cm
B. 11 cm
C. 13 cm
D. 15 cm

Answer

D

Explanation

`(Kq_(1)q_(2))/((0.15+h)^(2))=mg`
`h=0.15 m` or `15 cm`