Find the change in internal energy of a system which receives 70 J of heat from its environment and does 20 J of work.

Select one:

a. 90 J

b. 50 J

c. Zero

d. - 70 J

option B

Explanation:

given,

Q = energy input = 70 J

U = increase in internal energy

W is the work done = 20 J

using first law of thermodynamics

The change in internal energy of a system is equal to the heat added to the system minus the work done.

U = Q - W

U = 70 - 20

U = 50 J

The change in internal energy is equal to 50 J

Hence, the correct answer is option B