A body falling through a fluid reaches terminal velocity when
- A. the drag force becomes zero
- B. the upward drag and upthrust together balance the weight, so the net force is zero
- C. the body stops moving completely
- D. gravity stops acting on the body
Explanation
Drag increases with speed, so the body accelerates until the retarding forces grow to match its weight, after which the acceleration is zero and the speed stays constant. The body is still moving, and gravity still acts; what has vanished is the resultant force, not any individual one. This is why a raindrop reaches the ground at a survivable speed rather than accelerating for its whole fall.
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