Question

Figure display a closed cycle for a gas. From $c$ to $b,40J$ is transferred from the has as heat.From $b$ to $a,130J$ is transferred from the gas as heat, and the magnitude of the work done by the gas is $80J$. From $a$ to $c,400J$ is transferred to the gas as heat.what is the work done by the gas from $a$ to $c$?(Hint:you need to supply the plus and minus signs for the given data).

Answer 1

We note that there is work done in process $c\to b$, since there is no change of volume.
We also note that the magnitude of work done in process $b\to c$ is given, but
not its sign (which we identify as negative as a result). The total (or not) heat transfer is $Q_{net}=\left[\right(-40)+(-130)+(+400\left)\right]J=230J$. BY the First Lae of Thermodynamics(or, equivalently, comservation of energy), we have$Q_{net}=W_{net}$
$230J=W_{a\to c}+W_{c\to b}+W_{b\to a}$
$=W_{a\to c}+0+(-80J).$
Therefore, $W_{a\to c}=3.1\times {10}^{2}J>$