5. In the figure, two masses, \( M=16 kg \) and \( m=12.8 .0 kg \), are connected to a very light rigid bar and are attached to an ideal massless spring of spring constant \( 100 N / m \). The system is set into oscillation with an amplitude of \( 78 cm \). At the instant when the acceleration is at its maximum, the \( 16 kg \) mass separates from the \( 12.8 .0 kg \) mass, which then remains attached to the spring and continues to oscillate. What will be the amplitude of oscillation of the \( 12.8 .0 kg \) mass?
(a) \( 78 cm \)
(b) \( 62 cm \)
(c) \( 35 cm \)
(d) \( 98 cm \)