For a 2.2m long wood with uneven thickness, one end is placed on the ground, and the force of 680n is needed to lift its thick end; if the thick end is placed on the ground, the force of 420N is needed to lift its other end? (2) The position of the center of gravity of the wood

For a 2.2m long wood with uneven thickness, one end is placed on the ground, and the force of 680n is needed to lift its thick end; if the thick end is placed on the ground, the force of 420N is needed to lift its other end? (2) The position of the center of gravity of the wood

As shown in the right figure: the length of the wood is L = 2.2M, the distance between the center of gravity of the wood and the thin end is L1, and the distance from the thick end is L2; from the condition of lever balance, we can get: F1L = GL1, substituting into the data, we can get: 680n × 2.2m = g × L1 ① F2L = Gl2, substituting data: 420N × 2.2m = g × (2.2m-l1) ② A: (1) the weight of the wood is 1100n; (2) the position of the center of gravity of the wood is 1.36M from the thin end

Why can the fixed pulley change the direction of force and how to change it?
If there is a moving pulley in which the weight is placed on a horizontal plane, how to solve similar problems
It's a movable pulley that places the weight horizontally on the horizontal plane, and the spring pulls it. How to calculate the tension

First of all, for example, the flag pole is a fixed pulley. If you want to raise the national flag, do you want to pull it up to the top of the flag pole? So if you use the fixed pulley, the force you use is vertical and downward, which will change the direction of the force
Then, the work done by this pulling force is the spring scale indicator multiplied by the moving distance of the spring scale, which is twice the moving distance of the object
For example, when the pulley is moved, the object moves at a uniform speed of 1m under the tension of the spring scale, and the indication of the spring scale is 5N, then the work done by the tension of the spring scale is 5 * 1 * 2 = 10J

Physics problems in grade three of junior high school
There is a 2-meter-long wooden stick, thick at one end and thin at the other. It is just balanced when it is supported 0.8 meters away from the thick end. If it is supported in the middle and a weight of 8 N is hung on the thin end, the weight of the stick is () n

1*8=(1-0.8G
G=40