We will have the following:
First, we are told that the wind accelerates directly northwest, that means that the angle of inclination is 45°, so the following is true:
[tex]\begin{gathered} \sum F_x=115-75cos(45) \\ \\ \sum F_y=75sin(45) \end{gathered}[/tex]
Then:
[tex]\begin{gathered} v_f=\sqrt{(115-75cos(45))^2+(75sin(45))^2}\Rightarrow v_f=81.56229536... \\ \\ \Rightarrow v_f\approx81.6 \end{gathered}[/tex]
So, the magnitude of the final velocity is approximately 81.6 m/s.
