Your question was reviewed for reopening, and the reviewers unanimously voted to leave it on hold. Strictly speaking, that's why it wasn't reopened.
Now, to give a bit more detail, when I look at your question I basically see this structure:
[a homework problem]
I'm confused that internal forces changes kinetic energy with respect to center of mass frame or ground frame? I found a similar question here. But it didn't address my concern.
[some work toward solving the problem]
I'm stuck here and can't proceed further.
As mentioned in our policy on homework-like questions, we expect them to ask a specific conceptual question, not just ask how to solve the original homework problem or ask for help solving the problem. Basically, whatever difficulty you encountered in the process of solving the problem, you should ask how to get around that. That's the main thing you're missing that would motivate people not to reopen your question.