The following question has been closed with the explanation that it is in breach of the Homework Policy :
What will be the total work done by friction on the system (man+boat)?
However, it is not asking for a calculation nor is it asking someone to "do my homework".
It is clearly asking for a conceptual explanation of how internal friction relates to work done and kinetic energy. This difficulty has been raised in several similar questions but I have not found a clear and convincing answer on this site. The only answer to this question does not convince me, nor those who ask for more explanation in the comments.
Possibly this question is a duplicate of another - if so which one?
Possibly it could be closed as being unclear, because the problem itself is not sufficiently defined. But this can be easily rectified.
Please vote to re-open if you agree that this question deserves to have a good answer.