A solid insulating sphere of radius \(R\) has a non-uniform volume charge density \(\rho(r)\) and a total net charge of \(-Q\). A small particle of mass \(m\) and positive charge \(+q\) is released from rest at a distance very far from the sphere (\(r \to \infty\)). Assuming gravitational interactions are negligible, what is the speed of the particle when it reaches a distance \(r = 2R\) from the center of the sphere?