SAT Subject Physics Practice Question 134: Answer and Explanation
7. Through a series of thermodynamic processes, the internal energy of a sample of confined gas is increased by 560 J. If the net amount of work done on the sample by its surroundings is 320 J, how much heat was transferred between the gas and its environment?
A. 240 J absorbed
B. 240 J dissipated
C. 880 J absorbed
D. 880 J dissipated
E. None of the above
Correct Answer: A
By convention, work done on the gas sample is designated as negative, so in the first law of thermodynamics, ∆U = Q – W, we must write W = –320 J. Therefore, Q = ∆U + W = 560 J + (–320 J) = +240 J. Positive Q denotes heat in.