Red Solution explanations

Blue Solution explanations

A student pointed out that the wording on one of the questions was confusing: the ``work done by the piston" meant the work done by the gas, transferred through the piston, on something else (so positive if the gas expands). In other words, the same kind of work, and same sign convention, that we have been consistently using in the first law of thermodynamics, and every class example and homework exercise. But the wording might have given the impression to some that I was trying to be tricky, and asking about the opposite sign work. Let me say flat out, that I am not into trick questions with the wording. If you think a question might be a trick, because of the wording, I can guarantee you that it's not. Please always ask the TAs or proctors during the exam for clarifications on the wording if needed. In any case, I will accept either sign answer for the "work done by the piston" question.