Two small masses $$m$$ and $$M$$ lie on a large horizontal frictionless circular track of radius $$R$$. The two masses are free to slide on the track but constrained to move along a circle. Initially the two masses are tied by a thread with a compressed spring between them, with the spring of negligible length being attached with neither mass. The compressed spring stores a potential energy $$U_0$$. At time $$t=0$$ the thread is burnt and the two masses are released to run opposite to each other leaving the spring behind. The total mechanical energy remains conserved. On the circular track the two masses make a head on perfectly elastic collision. Take $$M=2m$$ for all calculations. Which options are correct