A metal block is hung under the spring scale. When immersed in water, the indication of the spring scale is 10N, and the density of the metal block is 3 × 103kg / m3, then the gravity of the metal block

A metal block is hung under the spring scale. When immersed in water, the indication of the spring scale is 10N, and the density of the metal block is 3 × 103kg / m3, then the gravity of the metal block

Let the volume of the metal block be v
Then the gravity of the metal block should be g = mg = ρ VG = 30000v
When immersed in water, the buoyancy f = ρ water GV = 10000v
Immersion in water, the force balance of the metal block, set the tension of the spring scale as t, then there is
T + F buoyancy = g
10+10000V=30000V
The solution is v = 5 * 10 ^ - 4 m ^ 3
Then the gravity of the metal block g = 30000v = 15N

Hang an object on the spring scale, the indication is 2n, if it is immersed in water, the indication of the spring scale is 1.5n, then the volume of the object is () m3, the density of the object
（）kg/m3

G=mg
m=G/g=2N/10N/kg=0.2kg
F = 2-1.5 = 0.5N
F floating = P water GV drainage
V row = V material = f float / P water g = 0.5 / (1.0 * 10 ^ 3 * 10) = 0.5 * 10 ^ (- 4) m ^ 3
P substance = m / V substance = 0.2kg/0.5 * 10 ^ (- 4) m ^ 3 = 4 * 10 ^ 3kg / m ^ 3

When a substance is immersed in water, the indication of spring scale is 4 / 5 of that in air

If F1 = Mg - ρ water VG = ρ VG - ρ water VG, F2 = ρ VG, so F1 / F2 = (ρ VG - ρ water VG) / ρ VG = (ρ - ρ water) / ρ = 1 - ρ water / ρ = 4 / 5, so ρ = 5, ρ water = 5 × 1 × 10 & # 179; = 5 × 10 & # 17