**Sample Problem Force And MOTION 11**

A raindrop with radius R = 1.5 mm falls from a cloud that is at height h = 1200 m above the ground. The drag coefficient C for the drop is 0.60.

SOLUTION: The Key Idea here is that the drop reaches a terminal speed v, when the gravitational force on it is balanced by the air drag force on it, so its acceleration is zero.

We next substitute this. the expression for A, and the given data into. Being careful to distinguish between the air density water density fl. we obtain,

SOLUTION: The Key Idea here is that, with no drag force to reduce the drop’s speed during the fall, the drop would fall with the constant free fall acceleration g, so the constant-acceleration equations .

CHECKPOINT 3: Near the ground, is the speed of large rain drops greater than, less than, or the same as the speed of small raindrops, assuming that all raindrops are spherical and have the same drag coefficient?

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