At present, a hot air balloon has a volume of 120m3. If the known air density is 1.29kg/m3, what is the buoyancy when it is still in the air A solid object with a volume of 10 negative quartic M & # 179; weighs 2.8n. If the object is completely immersed in a certain liquid, the apparent number of the spring dynamometer is 1.8n, then what is the density of the liquid?

At present, a hot air balloon has a volume of 120m3. If the known air density is 1.29kg/m3, what is the buoyancy when it is still in the air A solid object with a volume of 10 negative quartic M & # 179; weighs 2.8n. If the object is completely immersed in a certain liquid, the apparent number of the spring dynamometer is 1.8n, then what is the density of the liquid?

Front question: v = 120 m3, ρ air = 1.29 kg / m3
The buoyancy of the balloon is f floating = ρ air * g * V row = ρ air * g * V = 1.29 * 10 * 120 = 1548 n
The following supplementary questions:
From the point of view, the object is hung by a spring dynamometer
V = 10 ^ (- 4) m3, g = 2.8n, FRA = fshowing = 1.8n
Let the density of liquid be ρ liquid,
Analysis of the object: by gravity g, pull f pull, buoyancy f floating. Because it is static, so the resultant force is 0
We get f floating + F pulling = G
ρ liquid * g * V + FRA = g
ρ liquid * 10 * 10 ^ (- 4) + 1.8 = 2.8
The density of liquid is ρ liquid = 1 * 10 ^ 3kg / m3 (water)