Answer : [tex]U_f=2500\ J[/tex]
Explanation :
It is given that,
Heat that enters the system, Q = 1000 J
Work done by the system, W = -500 J
Initial internal energy [tex]U_i=2000\ J[/tex]
We know from first law of thermodynamics:
[tex]\Delta U = U_f-U_i=Q+W[/tex]
So, final internal energy will be :
[tex]U_f-2000\ J=1000\ J-500\ J[/tex]
[tex]U_f=2500\ J[/tex]
So, the final internal energy of the system is 2500 J.