A ladder of length l=12 m and mass m=45 kg lean against a wall (no friction between the wall and the ladder). The ladders upper end is at height h= 9.3 m above the pavement and which the lower end is supported (the pavement is not frictionless). The ladder’s center of mass is L/3 from the lower end along the lengthy of the ladder. A fire fighter of mass M=72 kg climb the ladder until her center of mass is L/2 from the lower end. What are the magnitude of the forces on the ladder from the wall and the pavement?

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explanation:

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.