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Home Minds On Newton's Laws Mission NL11 Air Resistance Help Help 7

Mission NL11 Air Resistance

The Question

A falling object has just reached terminal velocity. Which of the following statements are true of the object? ...

Define Help

Definition of Terminal Speed:
Terminal speed (sometimes called terminal velocity) is the final speed to which an accelerating object (usually a falling object) can accelerate.

Minds On Time

Many things will change as an object falls. Success on this question requires that you think about changes that occur over the course of time. That is, you must think about how quantities like speed, air resistance, net force and acceleration change as time changes. Changes in quantities as time changes - that's a lot of change and the very thing that makes this question difficult.
 
As an object falls, its speed increases due to the net downward force and the downward acceleration. The air resistance force is an upward force that is dependent upon the object's speed. As speed increases, the upward force increases as well. As this upward air resistance force grows in size, it begins to approach the same size as the downward gravity force. Thus, the growth in the air resistance force leads to a decrease in the net force and a decrease in the acceleration. Eventually, the upward air resistance force will equal the downward force of gravity. At this point, there is a balance of forces. Since the forces balance, the net force is 0 N and the object stops accelerating. The speed will no longer increase. The object has reached terminal speed or terminal velocity.

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