Xiao Jie found a metal block, and he wanted to know its gravity and density. He only had a spring scale with small range in his hand. When he used the spring scale to measure the gravity of the metal block, he found that it had exceeded the maximum range of the spring scale, so he designed the device as shown in the figure to measure. In the figure, OA: OB = 1:3, the metal block was suspended at point a with a string, and the spring scale was used at point B When a vertical upward force is applied, when the OB lever is horizontally stationary, the reading of the spring scale is 1.8n. When water is added to the container and the metal block is immersed in water, the reading of the spring scale is 1.2N, G is 10N / kg? (2) What is the buoyancy of a metal block when it is immersed in water? (3) What is the density of the metal block?

Xiao Jie found a metal block, and he wanted to know its gravity and density. He only had a spring scale with small range in his hand. When he used the spring scale to measure the gravity of the metal block, he found that it had exceeded the maximum range of the spring scale, so he designed the device as shown in the figure to measure. In the figure, OA: OB = 1:3, the metal block was suspended at point a with a string, and the spring scale was used at point B When a vertical upward force is applied, when the OB lever is horizontally stationary, the reading of the spring scale is 1.8n. When water is added to the container and the metal block is immersed in water, the reading of the spring scale is 1.2N, G is 10N / kg? (2) What is the buoyancy of a metal block when it is immersed in water? (3) What is the density of the metal block?

(1) If the lever is in balance under the pull of spring scale and the pull of weight on a, it can be obtained from the moment balance: F 1 · 0b = FG · OA, then FG = oboa, F 1 = 3 × 1.8n = 5.4n; because the metal block is in balance due to gravity and tension, so the gravity of the metal block g = FG = 5.4n; (2) after immersion in water, by force