A Level Physics Practice Exam

When a parachutist reaches terminal velocity, they are in a state of free fall where the forces acting on them are balanced. Initially, as they fall, the force of gravity pulls them downward, causing them to accelerate. However, as their speed increases, so does the air resistance acting in the opposite direction. Terminal velocity occurs when the downward force of gravity becomes equal to the upward force of air resistance.

At this point, the net force acting on the parachutist is zero, resulting in no further acceleration; the parachutist continues to fall at a constant speed, known as terminal velocity. This phenomenon is a direct consequence of Newton's second law of motion, where an object will continue to accelerate until the forces acting upon it are balanced.

Understanding this balance of forces is crucial in dynamics, highlighting the significant role that air resistance plays in free fall scenarios. Other options relate to factors that are either inaccurate or not directly responsible for achieving terminal velocity. Thus, the balance of gravity and air resistance is the core concept explaining why a parachutist reaches terminal velocity.