What is the change in internal energy if 60 j of heat are added to a system and the system does 40 j of work on its surroundings? use u = q - w.

U = 20 J

Explanation:

As per first law of thermodynamics we know that thermal energy given to the system is used to do some work by the system and also it is used to increase the internal energy of the system

So we can say that

here we know that

also we have

now from above equation we have