3.2.3—Objects moving against a resistive force may reach a terminal (constant)

Terminal velocity is reached when acceleration becomes zero, so the upward resistive force equals the downward weight and velocity becomes constant.

Find the terminal condition from ΣF=0, not from v=0. The object may approach terminal speed asymptotically rather than reach it in finite time.

For linear resistance kv, terminal speed is mg/k; doubling mass doubles terminal speed if k is unchanged.

Terminal velocity is not the same as zero velocity, and constant velocity means zero resultant force, not zero forces.