A vertical spring with a spring constant of 1575 m/N is compressed 0.25 m. A 250 g ball is placed on top of the spring. a. How much work was done to compress the spring? [49J]
b. What is the maximum height the ball can attain from the level of the uncompressed
spring? [20. m]
c. What is the maximum speed of the ball? [20. sm]

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.