The second interview can be tough. Be ready for questions that are designed to trick you a bit.

For example, one question was to consider a refrigeration unit that is infinitely efficient and left open inside of a room that is perfectly insulated. Will the temperature change?

Talk through your answers and ask clarifying questions clearly. I will note that with these very theoretical questions, you need some assumptions to solve them. I would have thought that you would need to ask about potential assumptions, but my interviewer seemingly did not like that.

See the above question in the interview process.