A = \frac{F b}{2} = \frac{m g b}{2} = \frac{ρ V g b}{2} = \frac{ρ g a b^{2} c}{2} = 1, 2 \cdot 10^{5} J

${A =\frac{Fb}{2}=\frac{mgb}{2}=\frac{\rho Vgb}{2}=\frac{\rho gab^2c}{2}= 1,2 \cdot10^5 J}$