Final answer:
Raindrops falling vertically appear to move diagonally to an observer in a moving car due to the concept of relative velocity, combining the vertical fall and the car's horizontal motion.
Step-by-step explanation:
When raindrops are falling vertically and you are observing them from a car that is moving horizontally, the motion you see is the combination of the raindrops falling and the motion of the car. From your perspective inside the car, the raindrops will appear to be moving diagonally because you are viewing the vertical fall of the rain through a frame of reference that is moving horizontally. This is related to the concept of relative velocity, where the observed velocity of an object depends on the observer's own velocity.
In the example provided, raindrops fall vertically at 4.5 m/s relative to the Earth. If an observer is in a car moving at 22.0 m/s straight, the velocity of the raindrops relative to the observer will not just be 4.5 m/s downwards, but will also include the horizontal velocity of the car. Therefore, the observer will measure the velocity of the raindrops as having both a vertical and a horizontal component, resulting in a diagonal path.