A Navy Seal of mass 80 kg parachuted into an enemy harbor....

A Navy Seal of mass 80 kg parachuted into an enemy harbor. At one point while he was falling, the resistive force of air exerted on him was 520 $\mathrm{N}$ . What can you determine about his
motion?

Key Concepts

Gravitational Force

Gravitational force is the force that pulls objects toward the center of the Earth. It is calculated as the product of an object's mass and the acceleration due to gravity, resulting in a force that acts downward. This force is crucial for understanding the motion of falling bodies since it provides the primary driving force for the descent.

Air Resistance

Air resistance, also known as drag, is a force that opposes the motion of an object moving through air. It acts in the opposite direction to the object's velocity and increases with speed. In the context of falling bodies, air resistance serves to slow down the acceleration caused by gravity, and its magnitude depends on factors like the object's shape, size, and speed.

Net Force and Acceleration

The net force on an object is the vector sum of all forces acting on it and determines the object’s acceleration according to Newton's Second Law (F_net = m * a). When an object is subject to both gravitational force and air resistance, the net force is the difference between these opposing forces, which in turn dictates whether the object is accelerating, decelerating, or moving at constant speed.

Terminal Velocity

Terminal velocity is reached when the force of air resistance equals the gravitational force, resulting in zero net force and, consequently, zero acceleration. At this point, even though the object is still moving, its speed becomes constant. In problems involving falling bodies, recognizing when terminal velocity occurs is key to understanding the dynamics of motion under air resistance.

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