No doubt. It depends on where you want to intrude real physics into the game.
If they didn’t intrude at all, the brick would be treated as an improvised thrown weapon, probably the equivalent of a thrown club. I’m not that familiar with D&D rules of combat, but it wouldn’t do very much damage. The fact that it just traveled almost 10 miles in 6 seconds would be irrelevant, and as far as I can tell, even the strength of the last guy in line would make no difference.
At combat readiness, yes. When your castle is under siege, you’re likely to hunker down for days at your station. Not knowing when the next attack will come, are you going to unload your steel crossbow that takes one minute to wind up?
Unload? Yes. Decock? No.
The game has limits on reality. For instance, letting everyone have an action for each “turn”. Hell, dividing into “turns”. Calling a turn a 6 second window of action doesn’t really help. You have six seconds to coordinate moving however many people into place and then try handing off a brick from one to another down the line. Okay, take 6 seconds to tell everyone to get into place, 6 seconds to line everyone up, then 6 seconds to start passing the brick. Even in 3 turns there’s still a very hard limit on how many people can pass that brick in 6 seconds. But the rules say everyone gets an action.
Reality says their action that 6 seconds may be waiting for the brick to get to them.
If a GM is trying to inject “reality” by applying physics of momentum from passing the brick, then he needs to step back and apply a stronger “reality” of effort it takes to do something and time it takes to take an action. Unless he’s going for silly fun over “reality”.
Right. It’s totally ok to try to roughly apply real life physics to a game. However, when you get unrealistic results (such as the peasant railgun), the reason is because you selectively applied physics to only one aspect.
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You have six seconds to coordinate moving however many people into place
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Oh that’s no problem : talking is a free action 
Naturally. All in the name of [del]Liberty[/del] the Funny. The PRG isn’t something that happened in a game or that a GM set up trying to add realism to his game - it’s patently absurd.
I can see cocking it when I go on watch. I’d hold off on loading a quarrel / bolt until it was needed, though. I can’t imagine that taking much time or effort, or making much noise.