Why do empty rooms sound hollow

Every empty room has echo, it's material does that. The object in the room take away that echo.

Explanation:

An empty room has nothing but hard walls. We know that hard substances reflects the sound . If the distance between you and walls is 17 meter than the sound will echo but if the distance is less than 17 meter than the sound will reverberate . So the empty room sounds hollow.

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.