Question

A thermodynamic system is taken through the cyclic PQRSP process. The net work done by the system is:

• A. $20J$
• B. $-20J$
• C. $400J$
• D. $-374J$

Answer 1

The correct option is A $20J$

$QR$ and $SP$ are two isochoric processes, so, work done for these two is zero.

Workdone $=W\cdot dV$

Workdone in $PQ$ path,

$W_1=100\times {10}^3\times (300-100)\times {10}^{-6}$

$W_1=20J$

Work done in $RS$ path,

$W_2=200\times {10}^3\times (100-300)\times {10}^{-6}$

$W_2=-40J$

$\therefore$ Net workdone= $W_1+W_2$

$W=-20J$

$-VE$ sign implies that work is done by the system.

$\therefore$ Workdone by the system is $20J$