Question

A heat engine undergoes a process in which its internal energy decreases by $400J$ and it gives out $150J$ of heat. During the process

• A. It does $250J$ of work and its temperature rises
• B. It does $250J$ of work and its temperature falls
• C. It does $550J$ of work and its temperature rises
• D. It does $550J$ of work and its temperature falls

Answer 1

Answer: (B)

It does $250J$ of work and its temperature falls

The internal energy of the system will decrease when the system does work and/or gives off heat. Since the heat given out is 150 J and the reduction in internal energy is 400 J, the work done by the engine is 400– 150 = 250 J.

When the internal energy is reduced, the system is cooled. Therefore, temperature will decrease.