Final answer:
A skydiver descending with a constant velocity is affected by the forces of gravity and air resistance. At terminal velocity, these forces are in equilibrium, resulting in a constant velocity.
Step-by-step explanation:
When a skydiver is descending with a constant velocity, there are two forces acting on them: gravity and air resistance. To draw a free-body diagram, we represent these forces as arrows. The force of gravity points downward while the force of air resistance opposes the motion and points upward. It should be noted that at terminal velocity, the magnitude of the force of gravity and the force of air resistance are approximately equal, resulting in a constant velocity.