石块质量m= G g = 5 10 kg=0.5kg.F浮=G-G1=5-3=2N,∵F浮=ρ水gV,∴V= F浮 ρ水g = 2 104 m3=2×10?4m3.∴ρ石= m V = 0.5 2×10?4 kg/m3=2.5×103kg/m3.在液体中所受浮力F=G-G2=5-2=3N.又∵F=ρ液gV,∴ρ液= F Vg = 3 2×10?4×10 kg/m3=1.5× 103kg/m3故答案为:2.5×103.1.5×103.