Answer
Volume $=0.240\text{ mi}^{3}$
$\textstyle W=4.41\times10^{5}\text{ lb}$
Work Step by Step
(a) Volume $=1(\mathrm{~km})^3=10^9 \mathrm{~m}^3$
$1 \mathrm{~m}=3.281 \mathrm{ft}$
$$
\begin{aligned}
\text { Volume } & =\frac{\left(10^9 \mathrm{~m}^3\right)\left(3.281 \frac{\mathrm{ft}}{\mathrm{m}}\right)^3}{\left(5.280 \times 10^3 \frac{\mathrm{ft}}{\mathrm{mi}_{\mathrm{i}}}\right)^3} \\
& =0.240 \mathrm{mi}^3
\end{aligned}
$$
b) ${W}$=${\gamma Volume}$
${\gamma }$=${\rho g }$$=\left(0.2 \frac{\mathrm{g}}{\mathrm{m}^3}\right)\left(10^{-3} \frac{\mathrm{kg}}{\mathrm{g}}\right)\left(9.81 \frac{\mathrm{m}}{\mathrm{s}^2}\right)=1.962 \times 10^{-3} \frac{\mathrm{N}}{\mathrm{m}^3}$
${W}$=$\left(1.962\times10^{-3}{\frac{\mathrm{N}}{\mathrm{m^{3}}}}\right)\left(10^{9}\mathrm{m^{3}}\right)=1.962\times10^{6}\mathrm{N}$
=$(1.962\times10^{6}{\bf N})\left(2.248\times10^{-1}{\frac{\mathrm{b}}{\mathrm{N}}}\right)=4.41\times10^{5}\text{ lb}$
