Three designs are proposed for an engine which is to operate between 300 K and 500 K. design A is claimed to produced 3000 J of work per kcal of heat input, B is claimed to produced 2000 J and C , 1000 J. which design would you choose ? Given 1 kcal =4185 J

Options

A. A only
B. B only
C. All
D. C only

Answer

D

Explanation

Maximum value of efficiency, `eta=1-(T_(2))/(T_(1))=1-(300)/(500)=(2)/(5)`
As, `eta=(W)/(Q_(1))`
`W=etaQ_(1)=(2)/(5)xx1000" cal "=400xx4.2J=1680J`
As no engine can produce more than 168000 J , designs A and B are not possible . Only design C is possible.