Role playing, or 'what if' scenarios are an opportunity for you to get your brain into gear and apply your intelligence and imagination to the situations you are presented with. If you trot out a series of pat answers that you've learned from elsewhere, it is very obvious to the interview board, and really does you no favours.
Why don't you sit down and think carefully about those situations for yourself, and come up with a range of options for each one. Then think about the pros and cons of each option, and be prepared to justify why you have chosen the course of action you say you would take. If you can't explain why you would do something, then how can I (the interviewer) be persuaded that you've thought about it at all?
Scroggs