Continuity mistake: When McCoy places the old tricycle down on the ground, the handlebars are facing the right with its wheels facing the left. When McCoy is attacked by the diseased Only, Kirk and Spock subdue him, and as he lies on the ground the tricycle flips over between shots, so the handlebars suddenly end up facing the left. (00:04:30)
Continuity mistake: After the wild man is down on the mound, his right hand is under his body. In the close up, it's on the frame of the trike. (00:05:05)
Continuity mistake: The ropes tying Yeoman Rand to the chair keep changing positions (above her elbows or below her elbows) between shots. (00:39:40)
Chosen answer: If they're in orbit, they're being pulled along by the planet's gravity well, therefore, impulse engines would only be used for minor corrections and would be "on standby" while in orbit, but not active. (Like keeping your car idling without revving the engine and creating plumes of exhaust).
Captain Defenestrator
Thank you for the info.
Movie Nut