Question

You are in a hot-air balloon that, relative to the ground, has a velocity of 8.0 m/s in a direction due east. You see a hawk moving directly away from the balloon in a direction due north. The speed of the hawk relative to you is 2.0 m/s. What are the magnitude and direction of the hawk's velocity relative to the ground? Express the directional angle relative to due east.

Answer 1

\[\sqrt{a ^{2} + b ^{2}}\] will give you the relative velocity
the angle would be tan -1 (2/8), giving 14 degrees.

http://physics.bu.edu/~duffy/py105/RelativeV.html
read the website for better understanding of relative velocity