When the state of a gas adiabatically changed from an equilibrium state A to another equilibrium state B an amount of work done on the system is 35 J. If the gas is taken from state A to B via process in which the net heat absorbed by the system is 12 cal, then the net work done by the system is (1 cal = 4.19 J)

Options

A. 13.2J
B. 15.4 J
C. 12.6 J
D. 16.8 J

Answer

B

Explanation

In the first case adiabatic change
`DeltaQ =0, DeltaW=-35 J`
From 1st law of thermodynamics ,
`DeltaQ-DeltaU+DeltaW`,
or , `0=Delta-35`
`DeltaU=35J`
In the second case
`DeltaQ=12 cal =12xx4.2 J` = 50.4 J`
`Delta W =DeltaQ -DeltaU=50.54-35=15.4 J`