Four point positive charges are held at the vertices of a square in a horizontal plane. Their masses are `1kg, 2kg, 3kg, & 4kg`. Another point positive charge of mass `10 kg` is kept on the axis of the sqaure. The weight of their fifth charge is balanced by the electrostatic force due to those four charges. If the four charge on the vertices are released such that they can freely move in any direction(vertical, horizontal etc.) then the acceleration of the centres of mass of the four charges immediately after the release is (Use `g= 10m//s^(2)`)

Options

A. `10m//s^(2)` downward
B. `20m//s^(2)` downward
C. zero
D. `10m//s^(2)` upward

Answer

b

Explanation

The net electrostatic force on `10 kg` charge should be
`F_(e)= 100N` upwards
`:.` Net electrostatic force on remaining four charges `- 100N` downwards
`:.` Net force on remaining four charges`=` Net electrostatic `+` net weight`= 100N+100N= 200N` downward
`:.` Acceleration of centre of mass of the four charges immediately after the release
`=("Net Force")/("Net mass")= (200)/(10)= 20 m//s^(2)` downwards