An alpha particle with charge \(+2e\) is launched with initial kinetic energy \(K_0\) from a distance very far from a stationary gold nucleus of atomic number \(Z\) (charge \(+Ze\)). The alpha particle moves directly along a line toward the center of the nucleus. Which of the following expressions represents the kinetic energy \(K\) of the alpha particle when it is at a distance \(r\) from the nucleus?