装有少量细纱的长直平底玻璃管漂在水面上，

1．
侵入水中的体积是 5×10＾-4m＾2 * 0.1m = 5×10＾-5m＾3
所以所收的浮力 F=ρgV
因为竖直方向只受浮力和重力，所以(M+m)g = ρgV
(M+m) = ρV = 1000kg/m^3 * 5×10＾-5m＾3 = 0.05kg

所以玻璃管和细纱的总重是0.05kg

2.(M+m)g = ρ盐水gV'=ρ水gV
所以 ρ盐水 = ρ水 * V/V'= ρ水 * (sh)/(sh') = ρ水 * h/h' = 1000kg/m^3 * (0.1m)/(0.1m-0.01m) = 1.11×10＾3kg/m^3

1.V排=sh=5×10＾－4m＾2 * 0.1m = 5×10＾-5m＾3
因为玻璃管漂在水面上，则玻璃管和细纱的重力为:
G=F浮=G排=p水gv排=1000kg/m^3*10N/kg*5×10＾-5m＾3 =0.5N
2.在盐水中排开液体的体积是
V排盐=sh盐=5×10＾－4m＾2 *( 0.1m-0．01m )=4.5*10^-5m^3
玻璃管还是漂浮所以F盐浮=G=0.5N
F盐浮=p盐水gv排盐=p盐水*10N/kg*4.5*10^-5m^3=0.5N
p盐水=1.11*10^3kg/m^3