I think that may vary from relationship to relationship. Mine is fairly open, and I would have no problem expressing to Him that there's no way to do what He's asking- even in your situation, where the punishment is light. If it had been designed that way, it would've been to provoke a fight from me and it would've worked, heh. Double the punishment; double the fun!

In a more serious light, though- if the punishment was something that was really bad (the "d" word, or something really outside my comfort zone) I would also have no problem sitting Him down and explaining it- respectfully, of course. (I do not always fight, but it is frequently fun, in the right time/place.) I would ask Him to assess it and acknowledge that if He still felt it was possible for me to accomplish, I would look for guidance from Him. If He told me simply to find a way, I wouldn't know if it was a setup for failure or if He had a solution.

If, in the end, I could not accomplish it, I'd ask for His solution to the problem. If He had none, after telling me it was possible, that would be a breach of trust. If He'd told me to find a way and had no solution, then it would've been a setup.

Okay, I feel like I've been overly wordy in explaining this response to the situation, but I try to be clear. I hope it helps at least a little bit.