Answer:
Jack is serving as a confederate in Dr. Smith's experiment on motivation.
Explanation:
A confederate is a person or an individual who participates in a psychological experiment by pretending to be one of the research subjects or subject of study in the research or study. A confederate is hired for working in the experiment by the researcher, to test the conformity of the experiment of the research.
Therefore, Jack is serving as a confederate in Dr. Smith's experiment on motivation.