In thermodynamic process, pressure of a fixed mass of a gas is changes in such a manner that the gas molecules given out 20 J of heat and 10 J of work is done on the gas. If the internal energy of the gas was 40 J, then the final internal energy will be

Q: In thermodynamic process, pressure of a fixed mass of a gas is changes in such a manner that the gas molecules given out 20 J of heat and 10 J of work is done on the gas. If the internal energy of the gas was 40 J, then the final internal energy will be

(a) 30 J

(b) 20 J

(c) 60 J

(d) 40 J

Ans: (a)

Sol: ∆Q = – 20 J, ∆W = – 10 J, U_i = 40 J, U_f = ?

∆Q = ∆U + ∆W

∆Q = U_f – U_i + ∆W

-20 = U_f – 40 -10

U_f = 30 J