Two Body Oscillations

Masses of Blocks
Force constant = 10 N/m

Two masses attached to a spring are oscillating on a smooth horizontal surface. The spring is initially in an elongated state and pressing start button releases the masses. Graphs of position vs time of the two masses are shown. Notice that when the masses are unequal the frequencies of oscillations are same but the amplitudes differ.
Red dot is the position of the CM of the two masses.