All jokes aside, exercise reduces stress. Which can really affect your mental performance. I found that when I was working out consistently my academic scores were higher.
My number one tip to people going into university is to find time to workout 3 times a week to balance out the stress.
If they were, how would you know? Almost by definition, their interests do not incline towards physics and they spend little time on it (compared to whatever makes them a 'jock'). Even if they change their minds, it's a bit late - hard to become a top-notch physicist when you don't learn anything about it until you're 25 or 30 or something.
Cardiovascular exercise is best performed after a weightlifting session and provides additional benefits.