Two identical bodies of constant heat capacity Cp at temperatures T1 and T2 respectively are used as reservoirs for a heat engine. If the bodies remain at constant pressure, show that the amount of work obtainable is
W=Cp(T1+T2−2Tf),(13.43)
where Tf is the final temperature attained by both bodies. Show that if the most efficient engine is used, then Tf2=T1T2.