In the one pulley system when you move the Mass from The 20-centimeter Mark to the 15 centimeter mark it moves to my 5cm how far did you pull the string? 5 cm
10cm
15cm
20cm

5 cm

Explanation:

Remember that in the pulley system the rope moves the same distance in both ends of the pulley, what the pulley system does is creating a mechanical advantage which basically means that it takes less effort to pull than the actual effort it would take, so for example if you have to lift a box that is 800 N, with a pulley system and the mechanical advantage you'd have to pull with less force.

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.