A similar exam problem in AMA95 was to derive the hyperbolic transforms. The trick there was to know how the Fourier transforms (based on sine/cosine) were derived, and just substitute in sinh/cosh.
If you were a formula plugger or just memorized facts, you'd be dead in the water.
I actually loved my classical mechanics class. The professor was really good and in the homeworks he'd come up with creative problems. The hardest part was always starting. Once you could get the right setup then you could churn away like any other (maybe needing to know a few tricks here and there).
Coming over to CS I was a bit surprised how test based things were. I'm still surprised how everyone thinks you can test your program to prove its correctness. Or that people gravely misinterpret the previous sentence as "don't write tests" rather than "tests only say so much"
And I recall a sci-fi short story long ago, technological civilization on a single continent with a permanently clouded sky. They had not figured out they were living on a sphere, they were having trouble with train tracks mysteriously being the wrong distance and train passengers feeling light on the high speed trains. I didn't check the guy's math but it sure seemed right when the answers looked exactly like Einstein's equations even though the units were very different. (Limiting velocity = orbital velocity, the discontinuity being weightlessness.)