Test and analysis: (1) According to the relationship of F=G, calculate the pressure with formula F=pS, and get the gravity of counterweight A;
(2) In order to solve the tension of the object counterweight A, firstly, the force of counterweight A is analyzed. According to the object in equilibrium, the resultant force is zero, and the pressure of the counterweight A on the ground is calculated according to the formula F=PS obtained from the pressure formula P=.
(3) The gravity of the moving pulley D and the pulling force of the object counterweight A on the rope * * * have the same effect on the left end of the lever. It is required to solve the problem that the vertical downward pulling force exerted by Cheng Xiao at H point is T 2, and the gravity of the moving pulley needs to be analyzed twice, and the equation is listed according to the balance condition of the lever, and the equation set is formed by combining the relationship of F 1: F 2 = 20: 19.
(1) According to p=, g = f = p0s = 2.4×104pa× 5×10 ~ 2m2 =1.2×103n.
(2) When the vertical downward pulling force exerted by Cheng Xiao at point H is T 2, the force of static counterweight A is shown in figure 1:
Then: f a2 = f "= p2s = 4×103 pa× 5×10 ~ 2m2 = 200n.
∫G = T A2+F A2
∴t a2 =g﹣f a2 = 1200n﹣200n= 1000n.
When the vertical downward pulling force exerted by Cheng Xiao at point H is T 1, the stress of static counterweight A is shown in Figure 2:
Then: f a1= f ′ = p1s = 6×103 pa× 5×10 ~ 2m2 = 300n.
∫G = T a 1+F a 1
∴t a 1 =g﹣f a 1 = 1200n﹣300n=900n.
(3) The advantage of moving pulley D is to save half the effort. ∴ the pulling force of lever EH on e is F-pull 1 =.
The stress of Cheng Xiao itself is shown in Figure 3:
Then: T 1 =G ren -f 1.
The stress analysis of lever EH is shown in Figure A in Figure 4:
Balance in horizontal position. ∴ According to the lever balance condition: =.
Namely: =, substituted data: = ①.
Similarly, when the vertical downward pulling force exerted by Cheng Xiao at point H is T 2, the stress analysis of lever EH is shown in Figure 4:
Available: =, replace in data: = ②.
According to the meaning of the question: = ③.
By solving the equations composed of ① ② ③, we get:
G mobile =100n; f 1 = 200n； F2 = 190 Newton
Comments: This problem is a difficult calculation problem in mechanics, involving the synthesis of simple machinery (lever, pulley) and pressure. When solving the problem, pay attention to distinguish the research objects according to the stem of the problem, analyze their stress and then answer them one by one.