In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas release `20 J` of heat and `8 J` of work is done on the gas. If initial internal energy of the gas was `30 J`, what will be the final internal energy?

Options

A. 58 J
B. 18 J
C. 42 J
D. 2 J

Answer

B

Explanation

`dQ=-20J`
`dW=-8J` (on the gas)
`dU=dQ-dW`
`=-20+8`
=-12
`U_(r)=U_(i)+(dQ-dW)`
`=30-12`
=18 J