A: You are not wrong — that is correct. There's a correction note below the video where I noted the error (using 0.7 instead of 0.2), and if you carry the math through with the right value you get exactly the number you found.

A: I pushed back on including supporting topics problems for years because I wanted you focused on core HVAC topics, but after feedback I added them to round out coverage of what can appear on the exam. This one on vibration and force transmissibility is a good example of a mechanical engineering concept that occasionally shows up — learn the structure of the equation and know your search terms in the reference handbook.

A: I believe the reference handbook is wrong here — I cross-checked the MERM and other mechanical engineering references, and none of them include that r² term for force transmissibility problems. I went with the MERM approach, which is what I'd recommend. It's a known issue, so trust your other references on this one.

A: That's a reasonable heuristic but not airtight — the key is whether the excitation source is the foundation moving (base motion) or the machine itself vibrating on a stationary base (fixed base). Also, there's a known error in my solution for this problem: I mixed up ωF and ωN in the frequency ratio, and I also dropped one of the squares in the force transmissibility formula, which does impact the numerical answer. The correction is noted, so make sure you're using the fixed version.