a piece of copper weighing 300g is heated to 100°c and is then quickly transferred into a copper calorimeter of mass 10g containing 100g of liquid with unknown specific heat capacity. if the final temperature of the mixture is 40°c calculate the specific heat capacity of the liquid (room temparature is 10°c) (specific heat capacity of copper is 400jkg/1​

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.