Explanation
The position of centre of mass remains unaffected because breaking of mass into two parts is due to internal forces.
Centre of mass lies always on the line that joins the two particles.
For the combination cd and ab this line does not pass through the origin.
For combination bd, initially it passes through the origin but later on it moves toward negative x-axis.
But for combination ac it will always pass through origin. So we can say that centre of mass of this combination will remain at origin.
The velocity of the top point of the wheel is twice that of centre of mass and the speed of centre of mass is same for both the wheels (Angular speeds are different).
Angular velocity is related to the rotating body.
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