To defrost ice accumulated on the outer surface of an automobile windshield, warm air is blown over the inner surface of the windshield. consider an automobile windshield with thickness of 5 mm and thermal conductivity of 1.4 w/m·k. the outside ambient temperature is 210°c and the convection heat transfer coefficient is 200 w/m2·k, while the ambient temperature inside the automobile is 25°c. determine the value of the convection heat transfer coefficient for the warm air blowing over the inner surface of the windshield necessary to cause the accumulated ice to begin melting.

3.2x10^7

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.