A bus with a vertical windshield moves along in a rainstorm at speed v_b. The raindrops fall vertically with a terminal speed v_r. At What angle do the raindrops strike the windshield?

The figure below shows the velocity vectors of the bus and the raindrops. It is assumed that the raindrops fall at an angle with respect to the vertical direction.

To the driver of the bus, the raindrops not only have the vertical velocity component but also a horizontal component, in a direction opposite to the direction of velocity vector of the bus. Therefore, the raindrops will appear to move in a direction at an angle relative to the vertical and given by:

It is important to note that is also the angle between the velocity vector of raindrops from the reference frame of the driver in bus and the velocity vector from the reference frame of the person on ground.