
\documentclass{article}
\usepackage{siunitx}
\pagestyle{empty}
\begin{document}
\noindent\si{kg.m.s^{-1}}\\                
\si{\kilogram\metre\per\second}\\ 
\si[per-mode=symbol]{\kilogram\metre\per\second}\\
\si[per-mode=symbol]{\kilogram\metre\per\ampere\per\second}\\
\SI[per-mode=fraction]{1.345}{\coulomb\per\mole}
\end{document}
