Rain drops fall from a height of 1Km(approx) . v, speed just before reaching the the ground should be sq. root of 2x9.8*1000 =140 m/s. But it is not so otherwise it would have destructed so many things at this speed. Why the speed of rain is less than 140m/s.

Because after falling down a certain height, it attains terminal velocity, after which it moves with constant speed.

this is true when we consider effect of friction zero OR we consider ideal case. In reality, wind and other obstruction in between  affects the speed of rain.

It is because of the terminal velocity it attains, after which its velocity stops increasing further.

Because the viscosity of air is non-zero, a retarding force is experienced by the falling raindrop which is proportional to its speed.

When the upwards retarding force = downward force of gravity, the acceleration becomes zero from that time onwards and the raindrop falls with a constant velocity called the terminal velocity.

Very interesting application of terminal velocity due to which the motion of rain drop is unaccelerated after a while

the raindrop faces 2 types of forces one is the upward force and the other is the downward force.when downward force equals the upward force the raindrop attains a const. velocity as there is no imbalanced force to acclerate it which is called terminal velocity.

because as they fall their acts two forces one mg and other air friction after a certain interval net force becomes zero and the drop gets terminal velocity.