Four charges are rigidly fixed along the Y-axis as shown. A positive charge approches the system along the `X`axis with initial speed just enough to cross the origin. Then its total energy at the origin is

Options

A. zero
B. positive
C. negative
D. data insufficient

Answer

C

Explanation

There exists a point P on the x-axis (other than the origin). Where net electric field is zero. Onece the charge Q reaches point P, attractive forces of the two -ve charge will dominate and automatically cause the charge Q to cross the origin
Now if Q is projected with just enough velocity to each P, its K.E. at P is zero.
But while being attracted towards origin it aquires K.E. & hence its net energy at the origin's is positive (P.E. at origin =zero)