Question

What is the change in internal energy if 20 J of heat is released from a system and the system does 50 J of work on the surroundings?

a. -70 j
b. 30 j
c. -30 j
d. 70 j

Answer 1

OPTION - A

Change in energy given by :-

dQ = du + dw

dQ = -20 - (-50)

dQ = -70

Answer 2

Answer is A.

Both energy changes describe energy be lost from the system (in different forms - as heat or as work). The negative sign indicates loss.