A solid metal block with density of ρ is hung on the hook of the spring scale. When it is weighed in air, the indication number of the spring scale is F1. When half of the volume of the metal block is immersed in the air, the spring scale will display the number of F1 If the indication of the spring scale is F2, then when the metal block is completely immersed in the liquid, the indication of the spring scale is, what is the density of the liquid?

A solid metal block with density of ρ is hung on the hook of the spring scale. When it is weighed in air, the indication number of the spring scale is F1. When half of the volume of the metal block is immersed in the air, the spring scale will display the number of F1 If the indication of the spring scale is F2, then when the metal block is completely immersed in the liquid, the indication of the spring scale is, what is the density of the liquid?

Weighing method: F floating = G-F
(1) F floating = F1-F2 = P liquid GV discharge = 1 / 2p liquid GV material
The results show that p-liquid GV = 2 (F1-F2)
(2) F floating = F1-F3 = P liquid GV discharge = P liquid GV material
F3 = f1-p, liquid GV = f1-2 (F1-F2) = 2f2-f1
F1 = g = PGV
We obtain v = F1 / PG, and substitute it into formula (1)
Liquid p = (F1-F2) P / F1

It is known that the density of lead is 11.3 × 103kg / m3, the volume of a solid metal ball is 0.5dm3, and the mass is 3.9kg. What is the density of this metal ball? Is this metal ball made of lead?

The density of the solid ball ρ = MV = 3.9kg0.5 × 10 − 3m3 = 7.8 × 103kg / m3; because the density of lead is 11.3 × 103kg / m3, which is not equal to the density of lead, the shot put is not made of lead. Answer: the density of the metal ball is 7.8 × 103kg / m3; the shot put is not made of lead

Ten people cross the river by raft. The average weight of each person is 60kg. The raft is composed of logs with a volume of 0.1m3. If the wood density is 400kg / m3
At least one log root is needed to form the raft

The deadweight of each log is 0.1 * 400 * 10 = 400N
When completely submerged, the buoyancy is f = PGV = 1000 * 0.1 * 10 = 1000N
Can provide buoyancy is 1000-400 = 600N
So 60 * 10 * 10 / 600 = 10

The volume of a wood block is 200cm3, and its density is 0.8 × 103kg / m3. After immersing it in water, let go. Why can't the wood block be suspended in water? What is the volume of the wood in the water when it finally floats on the water and is still?

(1) The weight of wood block: M = ρ wood V wood = 0.8 × 103kg / m3 × 200 × 10-6m3 = 0.16kg; the gravity of wood block: g = mg = 0.16kg × 10N / kg = 1.6n; when the object is completely immersed, V row = V wood, the buoyancy when immersed in water: F floating = ρ water gvwood = 1.0 × 103kg / m3 × 10N / kg × 200 × 10-6m3 = 2n