u = 5.83
Explanation:
The magnitude of a vector [tex]\vec{u}[/tex] is
[tex]|\vec{u}| = \sqrt{u_z^2 + u_y^2} = \sqrt{(-5)^2 + (3)^2}[/tex]
[tex]\:\:\:\:\:\:\:= \sqrt{34} = 5.83[/tex]