If pv = 81, then $\frac{dp}{dv}$ at v = 9 is :
Answer & explanation
Correct answer: option 2
$p v=81 \Rightarrow p=\frac{81}{v} \Rightarrow \frac{d p}{d v}=-\frac{81}{v^2}$
⇒ For v = 9, $\frac{d p}{d v}=-\frac{81}{81}=-1$
Hence (2) is correct answer.