The acceleration due to gravity on the moon is 1.67m/s. What does it mean?

It actually is 1.67 m/s/s which means that if you are falling, the moon gravity will increase your falling velocity by 1.67 m/s every second.

If you are falling on the moon from a height. The speed at which you will be falling will increase by 1.67 m/s every second

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.

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.