F浮 = ρgV排 = 1000kg/m^3 * 10N/kg * 50cm^3 = 0.5N
因为木块漂浮在水面上 所受重力和浮力是平衡力 所以G = 0.5N = mg =>m = 0.05kg
ρ = m/V = 0.67g/cm^3