Walking with an Umbrella
You must know that if you are walking in the rain, it is convenient to tilt your umbrella slightly ahead, the angle depending on your velocity and the angle of the rain. Otherwise the umbrella does not do its work. Do not leave it at home!
The velocity of the walking person and the velocity of the raindrops are represented by vectors. The angle of the resultant is the angle that the umbrella must make with the horizontal.