An object following a straight-line path at constant speed a- has no forces acting on it
b- has a net force acting on it in the direction of motion
c- has zero acceleration
d- must be moving in a vacuum
e- none of the above

i cant see the choices man

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.

its c i just checked it