# Finding the velocity of wind that affects an airplane

1. May 30, 2010

### Drex7

1. The problem statement, all variables and given/known data
A small airplane flies at a velocity of 145 km/h toward the south as observed by a person on the gound. The airplane plot measures an air velocity of 172 km/h south. What is the velocity of the wind that affects the plane?

Beyond knowing the velocity of both the plane and the wind and that they are both vector quantities going in the same direction, I'm unsure where to go from there and how exactly to answer the question. My initial thought was that there would not be just a portion of the wind's velocity that would affect the plane's. 172 km/h seems too simple. Please help clarify, thank you.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. May 30, 2010

### irycio

I'm not really sure about what I'm going to say now, so please correct me, but in my opinion what the pilot can measure is the speed of the wind "in comaprison" (damn, my lack of english vocabulary is disturbing) to the plane. Imagine that it doesn't say "wind" in the exercise, but "another plane", and our pilot measures, that it's flying 172 km/h in the same direction he is. What velocity of the other plane would someone standing on the ground observe, if "our" plane was flying 145 km/h?

3. May 30, 2010

### tiny-tim

Welcome to PF!

Hi Drex7! Welcome to PF!
No, air velocity … also called airspeed … is the speed of the plane relative to the air (rather like the speed of a ship relative to the water).

(and yes, it is a stupid name, but you're going to have to put up with it! )