When the charges in the rod are in equilibrium, what is the magnitude of the electric field within the rod?

If we have equilibrium, the magnitude must be zero.

Explanation:

If the charges are in equilibrium, this means that the total charge is equal to zero.

And as the charges must be homogeneously distributed in the rod, we can conclude that the electric field within the rod must be zero, so the magnitude of the electric field must be zero

f is prop to m1xm2 double m1 double force

your answer is c! hope this : )