An ideal gas is taken through the cycle A → B → C → A, as shown in the figure. If the net heat supplied to the gas in the cycle is 5 J, the work done by the gas in the process C → A is         

For cyclic process. Total work done =$W_{AB}+W_{BC}+W_{CA}$

$W_{AB}=P∆V$

 = 10(2 – 1) = 10J  and 

$W_{BC}$ =0
(as V = constant)
From FLOT, 

Q = $∆U+∆W$=U + W

$∆$U = 0 (Process ABCA is cyclic)
Q =$W_{AB}+W_{BC}+W_{CA}$
 5 = 10 + 0 + $W_{CA}$

$W_{CA}$ = – 5 J