I'm looking for practical questions that lead to quadratic equations with negative discriminant. The pupils involved are 16 years old and technically educated. 

Abstract mathematic questions are quite easy to create, e.g. "We're looking for two numbers, whose sum is 5 and product 7", but I'd like 'real world' examples. 

I imagine that electrical calculations could probably be used, but I'm afraid I'm not technically educated myself (alas). 

**EDIT**

What I'm really looking for is an example where the question and the solutions to the equation are somehow 'connected' to the real world.