\documentclass[tikz]{standalone}

\usepackage{pgfplots}

\pgfplotsset{compat=1.14}

\begin{document}

\begin{tikzpicture}
    \begin{axis}[xmin=0, xmax=1, ymin=0, ymax=1, xtick={0}, ytick={0,0.755}, yticklabels={0,$mg/\alpha$}, width=10cm,, height=5cm, ymajorgrids]
        \addplot [domain=0:1, samples=100] {-9.81/(13)*exp(-x*(13))+9.81/(13)};
    \end{axis}
\end{tikzpicture}

\end{document}
