Why must an air traffic controller know a plane's velocity

1. In order to prevent collision

2. To be able to control free flow of air traffic

Explanation:

The reason why it's paramount for air traffic controller to know the velocity of a plane is to enable them to avoid or prevent collision of planes coming in opposite direction. Knowing the velocity of the plane by the air controller would also give the air controller a good insight of how the air traffic should flow in oder to avoid accidents and disorderliness.

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.