A sample of an ideal gas is taken through the cyclic process `abca` . It absorbs `50 J` of heat during the part `ab`, no heat during `bc` and rejects `70 J` of heat during `ca`. `40 J` of work is done on the gas during the part `bc`.
(a) Find the internal energy of the gas at `b` and `c` if it is `1500 J` at `a`.
(b) Calculate the work done by the gas during the part `ca`.

Options

A. `1590 J`
B. `1620 J`
C. `1540 J`
D. `1570 J`

Answer

A

Explanation

`DeltaW_(AB) = 0` as `V =consta nt`
`:. DeltaQ_(AB) = DeltaU_(AB) = 50J` (given )
`U_(A) = 1500J :. U_B = (1500+50)J = 1550J`
`DeltaW_(BC) = -DeltaU_(BC) = -40J` (Given)
`:. DeltaU_(BC) = 40J :. U_C = (1550+40)J = 1590J`.