Question

A charge of +2.4 × 10−9 C is placed at the
origin, and another charge of +4.2 × 10−9 C
is placed at x = 2.5 m.
Find the point (coordinate) between these
two charges where a charge of +3.1 × 10−9 C
should be placed so that the net electric
force on it is zero.

Answer 1

Since q1 and q2 are positive charges, q3 in its equilibrium position has to be between them at the distance “x” from the charge q1.
F1=F2.
Use Coulomb’s Law
F1= k•q1•q3/x²,
F2 = k •q2•q3/(r-x)²,
k•q1•q3/x²= k •q2•q3/(r-x)²,
q1 /x²= q2 /(r-x)².
Solve for “x”