①F浮=ρ水gV排=1.0×10^3kg/m^3×10N/kg×50×10^-6m^3=0.5N
②因为物体漂浮,所以G=F浮=0.5N
m=G/g=0.5N/(10N/kg)=0.05kg
③ρ木=m/V=0.05 kg/(50+25) ×10^-6]m^3=0.67×10^3kg/m^3