You are in a stopped car with a helium balloon floating in the passenger compartment. All the windows are closed. The car accelerates forward. With respect to the passenger compartment, does the balloon move forward, move backward, or stay stationary?

– Close Encounters with the Brainteaser Job Interview, John Kador [via Hiring Technical People]

I would hate to have to answer that question during a job interview. I have no idea what the balloon would do nor do I know how to work this out. Asking puzzles during interviews has become an accepted technique when interviewing technical people. I have used such questions in the past but prefer the sort that don’t have one correct answer. I’m interested in finding out how the candidate approaches problem solving, but if the candidate responds immediately with the right answer I don’t know if they made a lucky guess, have heard the question before, or are really bright.