Last week I had my first ever technical interview in my field. I was told ahead of time to bring “all my textbooks” and a paper and pencil. For better or for worse, the interview was to be on the phone. Since most of my core engineering class books are boxed up in the storage room behind the garage I lovingly refer to as *spidersville* I grabbed my Fundamentals of Engineering Exam reference book instead feeling this would have many of the basic equations. I tried to prepare beforehand by looking stuff up but found there’s not a lot of information online for mechanical engineers and technical interviews. So I figured the least I could do was keep notes about what I was asked and post it here later to give somebody else the heads up. Though I suppose this is the point where some pre-internet engineer whines about how such advantages were not available to him or her…sorry.

First the interviewer described a picture for me which was of course the classic pendulum. I had something like this sketched out on my paper.

First I was asked to do a free body diagram and solve for T, the tension on the string of my pendulum. It’s been a long time since I took dynamics but strangely enough the pendulum was still fresh in my mind from state space equations from controls and signals classes. I don’t have it in my sketch there, but was told the horizontal velocity component of my pendulum is v and the length of the string is l. Solve and you get T = mgcos(theta) + mv^2/l. Next I was asked when the tension would be the largest, and if the string breaks and you have to redesign it what elements would you change. I’ll leave that up to the reader (this isn’t an answer book afterall).

Next was a cantilever beam. I used to have a professor who had an interesting eastern European accent who used to say that word so beautifully…but back to the topic at hand. This was described to me and I was asked for the angle of deflection. I was hunting quickly through my book, though she offered to give me the equation if I could tell her what elements were in it. φ = Pl^3/3EI. Then I was asked what I and E were (I’ll leave that as a take home assignment here) and what could be changed to limit the deflection of the beam.

Next was the fluids portion, and very non-specific (this particular company/product has not much to do with fluids). Given a system that’s pumping an incompressible fluid from one location to another where you are asked to improve upon the design, what do you need to know about the system. Then assuming the system already exists, what could you change to improve the system?

Lastly an airplane (or other flying object) is flying at a certain velocity and certain altitude and drops a bowling ball out of a plane. If the plane was in a vacuum, what would happen to the bowling ball. If it’s not in a vacuum, what do you have to take into consideration? Then, when will it hit the ground (y=v0t + 0.5at^2) and solving for t you can solve for how far it will travel horizontally.

So that was my technical interview for young fresh mechanical engineers. I’ve heard rumors that some places will ask you to derive the Navier-Stokes equations and I know where I work a manager who used to give you the beam example and ask you to draw the bending moment diagram. Sometimes it feels a little strange to be asked basic dynamics questions when I have a decent amount of work experience under my belt none of which involves daily application of kinematics but I did enjoy some of the more conceptual or critical thinking aspects of it. I invite any other sprockets to share their interviewee or interviewing stories here for the intimidating technical interview. Or I guess all you non-mechanical folks can share your opinions as well.

Basic questions should form a basic part of an interview. We use it for both junior and senior candidates alike. Exhibit A: Mr. Flop from my 2nd postk on Engineer Blogs. Lots of on paper experience; little real-life knowledge.

Plus you can always work up to the really hard questions if they breeze through. Needs to be progressive testing.

I hate to be snarky. But if the plane were in a vacuum, it would follow the same trajectory as the ball.

I love Newtonian Mechanics. 🙂

It’s something that I’ve heard of in interviews but never actually knew someone who went through it. That’s pretty rough.

I’m not sure I would have even taken them seriously if they said “bring your books”.

Yes Jacob that was the idea for that part. Was asked first what happens to the ball when dropped in a vacuum, then a second portion to calculate its drop time and therefore the horizontal distance it covers when not in a vacuum but still negating for wind resistance.

I think Jacob’s point was that if the plane were in a vacuum it wouldn’t be able to generate any lift, so it would plummet to the earth along with the bowling ball =)

But i think, the question says that the plane was flying at a certain velocity in vacuum somehow. So dropping the ball will just make the ball fall down to the ground under gravity with the same horizontal velocity as the velocity of the plane. And i am sure to calculate the time when not in vacuum, you just have the equation S = 0.5*g*t^2, as initially the vertical velocity was 0. 🙂