Generally, if you're asking technical questions to an interviewing candidate, you need to be in a position to really understand what a competent solution looks like. You must also be able to ask probing questions to a candidate to really understand their thought processes, and to give them hints when they get stuck. Whether you're a technical manager or engineer, or just advising new interviewers, this section will advise you on how to format your technical questions.
No matter the type of engineer you're interviewing, it's good to have an easy warm-up question. Have a mechanical engineer sketch a simple free-body diagram and solve a given problem. Have a programmer write a function to calculate the circumference of a circle given the radius. You're not necessarily looking for whether the candidate can solve the problem or not; ideally, everyone you bring in will be good enough to solve a very simple question. You're looking for the speed...