A horizontal uninsulated steam pipe passes through a large room whose walls and ambient air are at 300 K. The pipe of 125-mm diameter has an emissivity of 0.85 and an outer surface temperature of 373 K. Calculate the rate of heat loss per unit length from the pipe

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.

the answer is 12 as i may remember

: )