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Aug14-11, 06:51 PM
HW Helper
P: 1,663
Entropy change of a hot, falling object

I agree with those results to the first decimal place (since I rounded off only at the end), so we get a net increase in entropy for the "universe" of 21.9 J/K .

It is a reasonable safe assumption that just about all of the potential energy change is transferred into heating the river. The "splash" at impact displaces water and ejects some of it upward (briefly), as well as producing (a minute amount of) acoustical energy. But since practically all the water falls back into the river, that mechanical energy winds up heating the river after all. (We can extend "the universe" to include the air over the river, but the tiny amounts of water scattered as microdroplets and vapor and of sound energy probably contribute additions to entropy scarcely worth pursuing...)