[tex]\displaystyle Se~da:\\ \\
V=500l=0,5m^3\\ \\
\rho=800\frac {kg}{m^3}\\ \\
pe=10\%\Rightarrow \eta=90\%=0,9\\ \\
m_u=?kg\\ \\ \\
[/tex]
[tex]\displaystyle Formule:\\ \\
\eta=\frac{m_u}{m_t}\\ \\
\eta=\frac{m_u}{\rho\times V}\\ \\
m_u=\eta\times\rho\times V\\ \\ \\
Calcule:\\ \\
m_u=0,9\times 800\times 0,5=360kg[/tex]