Where No Man Has Gone Before - S1-E4
Character mistake: When Sulu is explaining the mathematics of Gary Mitchell's powers getting stronger, he says they are increasing "Geometrically", and then uses the popular example of doubling a penny every day for a month. What Sulu is describing would actually be exponentially. (00:24:14)
Answer: Kirk was getting his physical and Dr. McCoy probably turned off communications, because if he hadn't, Kirk would have left and headed straight for the bridge, leaving McCoy irritated.