Question

A hollow metal having density 8g/cc weigh 40g and 20g in water .volume of internal cavity is

Answer 1

Weight in water:
F_water=F-F_A;

Weight in the air:
F=mg;

The force of extrusion (Archimedes):
F_A=ρ_water Vg;
F_water=m_water*g;
m_water g=mg- ρ_water Vg;

The total volume of a metal object:
V=(m-m_water)/ρ_water
The cavity volume is equal to the difference between the total volume and volume of the metal itself:
V_cavity=V-V_metal;
V_metal=m/( ρ);
V_cavity=(m-m_water)/ρ_water -m/( ρ)
V_cavity=15 g/cc