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11.Thermodynamics
normal
When a system is taken from state $i$ to state $f$ along the path $iaf,$ it is found that $Q = 50\, cal$ and $W = 20\, cal$. Along the path ibf $Q = 36\, cal$. Work done along the path $ibf$ will be ........... $\mathrm{cal}$

A
$6$
B
$16$
C
$66$
D
$14$
Solution
By first law of thermodynamics:
$Q=\Delta U+W$
In path iaf:
$50=\Delta U +20$
$\therefore \quad \Delta U =30$
As this change in internal energy is between $i$ \& $f$ and does not depend on path.
Therefore along path ibf:
$Q =\Delta U + W$
$36=30+ W$
$\therefore \quad W =6\,cal$
Standard 11
Physics