Ineed is urgent ! which of the following statements applies to the motion of a ball rising and then falling in free fall? i. the ball has constant acceleration as it moves upward. ii. the ball has constant acceleration at the top of its path. iii. the ball has constant acceleration as it moves downward. a.i onlyb. iii onlyc. i and iiid. i, ii, and iii 

D.  For any projectile motion, there is a constant downwards acceleration due to gravity at all instances.  This not to be confused with velocity, which changes due to gravity at every moment along the object's path.

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.