$ 解：V_铁=\frac {m}{ρ_铁}=\frac {1.58\ \text {kg}}{7.9×10^{3}\ \text {kg/m}^3}=2×10^{-4}\ \text {m}^3=0.2\ \text {dm}^3$
$ 是空心的$
$ V_空=V-V_铁=0.5\ \text {dm}^3-0.2\ \text {dm}^3=0.3\ \text {dm}^3$
$ m_水=ρV=1.0×10^{3}\ \text {kg/m}^3×0.3×10^{-3}\ \text {m}^3=0.3\ \text {kg}\\$
$ m_总=m+m_水=1.58\ \text {kg}+0.3\ \text {kg}=1.88\ \text {kg}$
