A metal wire has a circular cross section with radius 0.800 mm. You measure the resistivity of the wire in the following way: you connect one end of the wire to one terminal of a battery that has emf 12.0 V and negligible internal resistance. To the other terminal of the battery you connect a point along the wire so that the length of wire between the battery terminals is d. You measure the current in the wire as a function of d. The currents are small, so the temperature change of the wire is very small. You plot your results as I versus 1/d and find that the data lie close to a straight line that has slope 600 A⋅m. Required:
What is the resistivity of the material of which the wire is made?

The value is  

Explanation:

From the question we are told that

   The radius is  

   The voltage of the battery is  

    The slope is  

Generally the resistance is mathematically represented as

Generally the current is mathematically represented as

=>    

=>  

Comparing this equation to that of a straight line we see that the slope is  

So    

Here A is the cross-sectional  area of the wire which is mathematically represented as

=>      

=>          

So

=>  

=>  

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.