Math & Science ⇒ align* inside align*

[ghostanime2001]

How can I use align* inside another align* environment?

I want that little extra vertical space align* gives after this line to be maintained.

Code: Select all

&N=mg+F\sin\theta

Code: Select all

\documentclass[fleqn]{article}
\usepackage{enumitem}
\usepackage{fullpage}
\usepackage[margin=1in]{geometry}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{siunitx}
\pagestyle{empty}
\setlength{\mathindent}{0pt}
\setenumerate[2]{label=\alph*),leftmargin=0.5cm,itemsep=0pt,topsep=-0.5cm}
\setenumerate[1]{label=\arabic*.,leftmargin=0cm,itemsep=0pt,topsep=-0.5cm,start=4}
\nopagebreak
\begin{document}
\begin{enumerate}
\item
\raisebox{1.85ex}{\parbox[t]{1.4in}{\null\includegraphics[width=\linewidth]{diagram8}}}
\begin{minipage}[t]{0.9in}
$\begin{aligned}[t]
\theta&=\SI{15}{\degree} \\
F&=\text{300 N} \\
m&=\text{70 kg} \\
\mu_{s}&=0.4 \\
\mu_{k}&=0.28
\end{aligned}$
\end{minipage}
\begin{minipage}[t]{1.7in}
\begin{minipage}[t]{1.7in}
$\begin{aligned}[t]
&\sum F_{y}=0 \\
&N-mg-F\sin\theta=0 \\
&N=mg+F\sin\theta
\end{aligned}$
\begin{align*}
&F\cos\theta<f_{s,max} \\
&F\cos\theta<\mu_{s}N \\
&F\cos\theta<\mu_{s}(mg+F\sin\theta) \\
&(300)(\cos\SI{15}{\degree})<(0.4)((70)(9.8)+(300)(\sin\SI{15}{\degree})) \\
&289.8<305.46 \\
&\therefore F\cos\theta=f_{s,max} \\
&(300)(\cos\SI{15}{\degree})=f_{s,max} \\
&\text{289.8 N}=f_{s,max}
\end{align*}
\end{minipage}
\end{minipage}
$\begin{aligned}[t]
f_{s,Max}&=\mu_{S}N \\
f_{s,Max}&=\mu_{S}(mg+F\sin\theta) \\
&=(0.4)((70)(9.8)+(300)(\sin\SI{15}{\degree})) \\
&=\text{305.46 N}
\end{aligned}$
\end{enumerate}
\end{document}