Below the fixed end of the insulating horizontal thread, at a distance equal to the length (10 cm) of the thread there is a fixed charge, which has the same charge as the charge `(1 muC)` of the small body of mass m at the end of the thread as shown in the figure. The body is released and when it is at the lowest position the angle between the thread and the horizontal is `30^(@).` The mass of the moving body is closest to :

Options

A. 54 g
B. 108 g
C. 0.54 g
D. 10..8g

Answer

A

Explanation

By energy conservation ,
`mgl //2 = kQ ^(2) // l sqrt2 - kQ ^(2) //l`