Question

In a heat engine if 1000 j of heat enters the system the piston does 500 j of work, what is the final internal energy of the system if the initial energy was 2000 j ?

Answer 1

Answer : $U_f=2500\ J$

Explanation :

It is given that,

Heat that enters the system, Q = 1000 J

Work done by the system, W = -500 J

Initial internal energy $U_i=2000\ J$

We know from first law of thermodynamics:

$\Delta U = U_f-U_i=Q+W$

So, final internal energy will be :

$U_f-2000\ J=1000\ J-500\ J$

$U_f=2500\ J$

So, the final internal energy of the system is 2500 J.