I've had a coding interview (screen, not whiteboard) fail where the main criticism was that one routine detail I took a while to get right could have been googled faster. In hindsight I still doubt that, given all the semi-related tangents you end up following from Google, but that was their expectation, look up the right piece of example code and recognize the missing bit (or get out right immediately).

For a proper engineering question (as in not software), I'd expect the expected answer to be naming the reference book where you'd look up the formula. Last thing you want is someone overconfident in their from memory version of physics.