In the reference frame \(K\) two particles travel along the \(x\) axis, one of mass \(m_{1}\) with velocity \(\mathbf{v}_ {1}\), and the other of mass \(m_{2}\) with velocity \(\mathbf{v}_{2} .\) Find: (a) the velocity \(\mathbf{V}\) of the reference frame \(K^{\prime}\) in which the cumulative kinetic energy of these particles is minimum; (b) the cumulative kinetic energy of these particles in the \(K^{\prime}\) frame.