What is the acceleration of a 9.6-kg rock if gravity pulls it downward, but air resistance pushes upward with a force of 2.8 N?

OK, so the downward force on the rock is mg (force of g) - 2.8N (force in opposite direction). since mg (9.6 kg*9.8 m/s^2) = 94.08 N, then mg-2.8 = 91.28 N. That is your net force on the rock (or total force). And, since f=ma, a = f/m.

so, a = 91.28 N / 9.6 kg = 9.5 m/s^2. (final answer)