1)One of the most efficient engines ever built is a coal-fired steam turbine in the Ohio valley, driving an electric generator as it operates between 1870°C and 430°C.
(a) What is its maximum theoretical efficiency?
%
(b) Its actual efficiency is 42.0%. How much mechanical power does the engine deliver if it absorbs 1.4 105 J of energy each second from the hot reservoir?
kW
2) A 70-kg log falls from a height of 28 m into a lake. If the log, the lake, and the air are all at 303 K, find the change in entropy of the Universe during this process.
J/K
2 Responses
I liked the 2) part
1A. Max. theoretical (Carnot) efficiency = 1-T(cold)/T(hot) = 67.2 %. (T(cold) and T(hot) are of course in deg K.)
1B. That one you can do. 0.42*1.4E5.
2. The simplest solution (see ref.) is ΔS = ΔQ/T = mgh/T = 70*9.8*28/303 J/K.