1 Kg stone at `27^(@)`C falls 100 m into a lake whose temperature is `27^(@)` C. Find the entropy charge of (a) the stone (b) the lake (c) the univers when
(i) stone is lowered reversibly
(ii) stone is dropped freely
Compare the loss of available energy in two cases

Explanation

(i) If the stone is lowered reversibly no amount of heat will be produced. Also since term of stores remains
the same
`DeltaS_("stone") = 0`
`q_("rev")= 0 rArr DeltaS_("lake") = 0`
`and DeltaS_("total") = DeltaS_("universe")= DeltaS_("lake") +DeltaS_("stone")= 0`
(ii) If the stone is lowered irreversibly, the potenial energy will be entirely lose in form of heat energy
`q_("actual") = q_("irr") =mgh`
`DeltaS_("stone") = 0`
`DeltaS_("lake") =-(q_("irr"))/(T) = - ((-1 xx9.8 xx1000)/(300)) = (980)/(300)J//K`
`=3.26 J//K`
`DeltaS_("total") = 3.26 J//K`