This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
I would say that CPU memory is unpredictable, and you cannot tell whether it changes depending on size of documents. Similarly there are complicated algorithms about paging as already mentioned, so whether adding data to a document like that changes the proportion of RAM in use is again unpredictable. It is possible that increasing the size of the active document causes an inactive document to be paged, in which case adding those data causes a reduction in used RAM.
I think you need to work out a definitive answer, and I think it looks like this:-