Question:-
A control mass undergoes a process from state 1 to 2 as shown in the above figure. During this process, the heat transfer to the system is 200 KJ. If the control mass returned adiabatically. From state 2 to sate 1 by another process, k then the work interaction during the return process (in kN.m) would be

Option (A)
-400
Option (B)
-200
Option(C)
200
Option(D)
400
Correct Option:
(B)
Question Solution:
Since control man (so case of closed system) intercept of path on X-axis is the work done by the process

W = area of ΔA 12 + area of NA2CB
W = (1/2)x (3-1)x 200 + 100 x (3-1)
= 200+200=400kJ
W = (1/2)(300-100) x 2 + 100 x 2
= 200+200 = 400 kJ
\ From 1 ® 2
U1 + Q = U2 + W
U1 - U2 = W –Q = 400 – 200 = 200 kJ
From 2 ® 1
Work done will be same
Since adiabatic so Q = 0
U2 + Q = U1 + W
W = U2 - U1 =-(U1-U2) =- 200 KJ
question-answer-faq-3105