Chapter 11 - Section 11.2 - Vectors - Exercises - Page 608: 27

$5k$

Here, $v=0i+0j+5k$ and $|v|=\sqrt{0^2+(0)^2+(5)^2}=\sqrt {25}=5$ The unit vector $\hat{\textbf{v}}$ can be calculated as: $\hat{\textbf{v}}=\dfrac{v}{|v|}$ Now, $\hat{\textbf{v}}=\dfrac{0i+0j+5k}{5}=(0,0,1)$ Thus, $v=|v|\hat{\textbf{v}}=5(1k)=5k$