# Raindrops fall vertically relative to the ground at a speed of 35 m / s. What is the lowest ground speed a vehicle

**Raindrops fall vertically relative to the ground at a speed of 35 m / s. What is the lowest ground speed a vehicle must have so that the rear sight glass, tilted at 60 degrees to the horizon, does not leave drip marks? Disregard air turbulence.**

Given:

V = 35 m / s;

The angle is 60 degrees.

Decision:

In order to find the answer, you need to draw a triangle. In it, the speed of one raindrop relative to the vehicle speed a = vk – v will be taken as a.

It is important that the droplet speed vk is perpendicular to the machine speed v. This means that they form two perpendicular vectors.

We need no traces of drops left. To do this, it is necessary that a is parallel to the rear window (there is an angle of 60 degrees).

Then we find the tangent.

tg 60 = vk / v.

So v = vk / tg60.

Substitute the values we know and get the answer:

v = 35 / √ 3 = approximately 20.2 m / s

Answer: 20.2