## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Let $V_c$ be the volume of the cylinder. We can find the mass of the cylinder. $M = V_c~\rho_{steel}$ $M = (\pi)(0.05~m)^2(0.20~m)(7900~kg/m^3)$ $M = 12.4~kg$ The buoyant force on the cylinder is equal to the cylinder's weight $Mg$. The buoyant force is equal to the weight of the mercury that is displaced. Let $\rho_m$ be the density of mercury. We can find the volume $V_m$ of mercury that is displaced. $F_B = Mg$ $\rho_m~V_m~g = Mg$ $V_m = \frac{M}{\rho_m}$ $V_m = \frac{12.4~kg}{13.6\times 10^3~kg/m^3}$ $V_m = 9.12\times 10^{-4}~m^3$ We can find the height $h$ such that the bottom part of the cylinder has the volume $V_m$. $\pi~r^2~h = V_m$ $h = \frac{V_m}{\pi~r^2}$ $h = \frac{9.12\times 10^{-4}~m^3}{(\pi)~(0.05~m)^2}$ $h = 0.116~m = 11.6~cm$ The length of steel that is below the surface is 11.6 cm. Therefore, the length of steel that is above the surface is 20 cm - 11.6 cm which is 8.4 cm.