Q. In the thermodynamical process, pressure of a fixed mass of gas is changed in such a manner that the gas releases 20 J of heat and 8 J of work is done on the gas. if internal energy of the gas was 30 J, then the final internal energy will be
A) 42 J
B) 18 J
C) 12 J
D) 60 J
Explanation
(b) As $\mathrm{\Delta}U = \mathrm{\Delta}Q - \mathrm{\Delta}W$
$\mathrm{\Delta}U = ( - 20) - ( - 8) = - 12$ J
$\mathrm{\Delta}U = U_{f} - U_{i} = - 12$
$\therefore\ \ U_{f} = - 12 + U_{1} = - 12 + 30 = 18$ J
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.