<<echo=FALSE, results=hide>>=
typ <- if(match_exams_call() %in% c("exams2pdf", "exams2nops")) ".pdf" else ".svg"
sup <- c("image68_1.eps")
sup <- gsub(".eps", typ, sup, fixed = TRUE)
include_supplement(sup, recursive = TRUE)
@

\begin{question}
A very long cylinder with the cross-sectional area of an equilateral
triangle of side length $a$ and specific weight $\gamma_r$ is submerged. 
\begin{center}
   \includegraphics[scale=0.8]{image68_1\Sexpr{typ}}
\end{center}
The water pressure at the bottom is $u=\gamma_w \cdot \frac{\sqrt{3}}{2} a$.
The buoyancy force per linear meter of the cylinder is 
\begin{answerlist}
  \item $A_w = u \cdot a = \gamma_w \cdot \displaystyle \frac{a^2\sqrt{3}}{2}$
  \item $A_w = \gamma_w \cdot \displaystyle \frac{a^2\sqrt{3}}{4}$
  \item $A_w = (\gamma_r-\gamma_w) \cdot \displaystyle \frac{a^2\sqrt{3}}{4}$
  \item $A_w = \gamma_w \cdot a^2$
  \item $A_w = \gamma_w \cdot \displaystyle  a^2 \sqrt{\frac{3}{16}}$
  \item $A_w = \gamma_w \cdot \frac{\sqrt{3}}{2} a$
  \item $A_w = \gamma_w \cdot a \cdot \frac{1}{2} \left(\frac{\sqrt{3}}{2} a \right)$  
\end{answerlist}
\end{question}

\exname{Exercise 68 (groundwater)}
\extype{mchoice}
\exsolution{0100101}
\exshuffle{4}
\exextra[difficulty,numeric]{1}
\exextra[category,character]{groundwater}