解：$(1)F_浮=ρ_水gV_排=1.0×10^3\ \mathrm {kg/m}^3×10\ \mathrm {N/kg}×100×10^{-6}\ \mathrm {m^3}=1\ \mathrm {N} $
$(2)S=\frac {V_{排}}{∆h}=\frac {100\ \mathrm {cm}^3}{12\ \mathrm {cm}-10\ \mathrm {cm}}=50\ \mathrm {cm}^2$
$V_{水}=Sh_{水}=50\ \mathrm {cm}^2×10\ \mathrm {cm}=500\ \mathrm {cm}^3$
$m_{水}=ρ_{水}V_{水}=1\ \mathrm {g/cm}^3×500\ \mathrm {cm}^3=500\ \mathrm {g}$
$G_{水}=m_{水}g=0.5\ \mathrm {kg}×10\ \mathrm {N/kg}=5\ \mathrm {N}$
$(3)F=G-F_{浮}=3\ \mathrm {N}-1\ \mathrm {N}=2\ \mathrm {N}$
