Thermodynamics Question 140
Question: In a thermodynamics process, pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8J of work is done on the gas. If the initial internal energy of the gas was 30J. The final internal energy will be
[DPMT 2002]
Options:
A) 18J
B) 9J
C) 4.5J
D) 36J
Show Answer
Answer:
Correct Answer: A
Solution:
Given $ \Delta Q=-20J, $
$ \Delta W=-8J $ and $ U _{1}=30J $
$ \Delta Q=\Delta U+\Delta W $
Therefore $ \Delta U=(\Delta Q-\Delta W) $
Therefore $ (U _{f}-U _{i}) $ = $ (U _{f}-30)=-20-(-8) $
Therefore $ U _{f}=18J $
