Posted by Ashley on .
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.

physics 
Elena,
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/(rx)²,
k•q1•q3/x²= k •q2•q3/(rx)²,
q1 /x²= q2 /(rx)².
Solve for “x”