ANCPERS,
Here's another question for your physics grad student. Print it out and give it to her verbatim.
Assume that the terminal velocity of the lighter object is exactly 15.80 m/sec.
What will be the lighter object's acceleration when it is falling at 15.75 m/sec?
If you say it's acceleration is 9.8 m/sec/sec, how can aerodynamic drag be large enough to completely stop acceleration when the speed is 15.80 m/sec, yet have absolutely *no* effect on acceleration when it is falling 0.05 m/sec slower?
If you say that the acceleration will be less than 9.8 m/sec/sec, then *why* is it not accelerating at exactly g (9.8m/sec/sec) ?