"A proton has an initial speed of 4.9×105 m/s . Part A What potential difference is required to bring the proton to rest? Express your answer using two significant figures."

Explanation:

The kinetic energy will be converted into electric potential energy, so we write:

We want the potential difference needed for this to happen, which is:

Where m and q are the mass and charge of the proton. We then use values:

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.

a is the best answer your welcome