Two airplanes pass each other while flying at a constant altitudes. While they have identical airspeeds, their ground speeds are $v_1$ and $v_2$, respectively, and the angle between the velocity vectors is $\alpha$. Based on this knowledge, what is the minimal possible value
i
of the airspeed of the planes;
ii
of the wind speed at the altitudes of the planes?
iii
Answer the question ii) if now $v_1 = v_2 = v$, but it is known that the airspeed of one of the planes is two times bigger than that of the other.
