Two solid spheres of identical radius \(R\), Sphere 1 of mass \(m_1 = m\) and Sphere 2 of mass \(m_2 = 4m\), fall vertically through air. The air exerts a resistive drag force of magnitude \(F_D = D v^2\) on each sphere, where the drag parameter \(D\) is identical for both spheres, and buoyant forces are negligible. Both spheres eventually reach their respective constant terminal speeds. What is the ratio \(P_2 / P_1\) of the rate of mechanical energy dissipated by drag on Sphere 2 to that on Sphere 1 when both spheres are falling at their terminal speeds?