解：$(1)F_浮=ρ_水gV_排=1.0×10^{3}\ \text {kg/m}^{3}×10\ \text {N/kg}×100×10^{-6}\ \text m^{3}=1\ \text {N} $
$(2)S=\frac {100\ \text {cm}^{3}}{12\ \text {cm}-10\ \text {cm}}=50\ \text {cm}^{2}$
$V_{水}=50\ \text {cm}^{2}×10\ \text {cm}=500\ \text {cm}^{3}$
$m_{水}=ρ_{水}V_{水}=1 \ \text {g/cm}^{3}×500\ \text {cm}^{3}=500\ \text {g}$
$G_{水}=m_{水}g=0.5\ \text {kg}×10\ \text {N/kg}=5\ \text {N}$
$(3)F=G_{石}+G_{水}=3\ \text {N}+5\ \text {N}=8\ \text {N}$
$p=\frac {F}{S}=\frac {8\ \text {N}}{50×10^{-4}\ \text m^{2}}=1600\ \text {Pa}$
