%From Haynes lecture notes on 4

\rbqquest{In the cooling example the DE was:
\[\overdot x(t)=k(T_{\text{ext}}(t)-x(t)).\]
What does it mean for $k$ to be large?
}

\rbqchoice{\begin{enumerate}
\item good insulation
\item bad insulation
\item don't know
\end{enumerate}
}

\rbqans{When the insulation is good, $k$ is small; when the insulation is
  bad $k$ is large.  When the insulation is perfect $k$ is zero. $k$
  is a {\em coupling constant}; when it is zero, the temperature inside the
  cooler is decoupled from the temperature outside. In the
  construction industry a number like $k$ is pasted on windows; it's
  called the U-value of the window.}