Question

A water droplet starts falling from rest from a height H and acquires the terminal speed just before reaching the ground.If g is assumed to be constant and radius of drop is are the work done by air drag is ?

Answer 1

The rain drop falls because of gravity,they get accelerated towards earth ground at 9.8 m/s^2 and this acceleration is constant,but their are also many other forces acting upon the rain drop which resist the accelerating motion of the rain drop ,one of them is air resistance ,air resistance apply an opposing force or a force opposite in direction of that of acceleration due to gravity i.e.. its force is upwards on the rain drop .When these two forces ,acceleration due to gravity and force due to air resistance becomes equal on the rain drop the rain drop stops accelerating any further and achieves a constant velocity known as terminal velocity. For example one of your friend is pulling you on the left side with a certain force,you will be start moving towards left as he is pulling but then another friend of your's comes and from the same side he pushes you towards right with the same amount of force that the other friend is trying to pull you,what will happen you will stop moving because two equal in magnitude but opposing forces cancels each other. Why they are pulling you and pushing you I have no idea...

Reference https://www.physicsforums.com/threads/terminal-velocity-of-rain-drops.696592/