∴FLOB=GLOA，

Namely: 10N×0.4m=G×0.2m,

∴g=20n；

(2)∫G = mg = 20N，

∴m=Gg=20N 10N/kg=2kg，

∴ρ=mv=2kg 1× 10-3m3=2× 103kg/m3；

(3) When a vertically downward pulling force F'= 5N is applied to the B end,

The lever is balanced in a horizontal position,

∴f′lob=faloa，

Namely: 5N×0.4m=FA×0.2m,

∴FA= 10N，

At this time, the pressure of the object on the ground:

F pressure = g-fa = 20n-10n =10n.

Answer: (1) The gravity on the object is 20N；;

(2) The density of the object is 2×103 kg/m3; /m3；

(3) At this time, the pressure of the object on the ground is 10N. ..