# Classic rain falling on a car's window problem doubt

Calabi_Yau
A car travels due east with a speed of 50.0 km/h. Raindrops are falling at a
constant speed vertically with respect to the Earth. The traces of the rain on the
side windows of the car make an angle of 60.0° with the vertical. Find the
velocity of the rain with respect to (a) the car and (b) the Earth.

I got the right answer, I considered in (a) the x-component of v(rain) the same as the horizontal component of the car's velocity, and the by trigonometry calculated the y-component.

However, I have a doubt: If the rain has only vertical velocity relative to the car, why do the traces make an angle of 60º with the vertical? For me that must mean the rain has displacement relative to the car and thus the horizontal component of the rain's velocity relative to the car is not zero!

Could you clarify this to me?

## Answers and Replies

Mentor
A car travels due east with a speed of 50.0 km/h. Raindrops are falling at a
constant speed vertically with respect to the Earth. The traces of the rain on the
side windows of the car make an angle of 60.0° with the vertical. Find the
velocity of the rain with respect to (a) the car and (b) the Earth.

I got the right answer, I considered in (a) the x-component of v(rain) the same as the horizontal component of the car's velocity, and the by trigonometry calculated the y-component.

However, I have a doubt: If the rain has only vertical velocity relative to the car, why do the traces make an angle of 60º with the vertical? For me that must mean the rain has displacement relative to the car and thus the horizontal component of the rain's velocity relative to the car is not zero!

Could you clarify this to me?

The answer to your question is in the problem statement: "Raindrops are falling at a
constant speed vertically with respect to the Earth" (emphasis added).