Final answer:
An object falling at a constant speed of 100 mph has balanced forces acting on it: the force of gravity and air resistance are equal, resulting in a net force of zero and terminal velocity.
Step-by-step explanation:
When an object is falling through the air at a constant speed of 100 mph and experiences air resistance, it indicates that the forces acting upon the object are balanced. In this scenario, the force of gravity, which pulls the object downward, is equal in magnitude but opposite in direction to the force of air resistance pushing upwards against the object. Since the object is moving at a constant speed, the overall net force acting on the object is zero, meaning the forces are in balance. Thus, the object has reached what is known as terminal velocity, where the downward force of gravity is exactly balanced by the upward force of air resistance, resulting in no acceleration and a constant velocity.