Many theories about atomic structure have molded the current view of the
atom. the quantum model suggests that electrons

Orbit around the nucleus at specific energy levels

Explanation:

In the quantum model of the atom (Bohr's model), electrons orbit the nucleus at specific orbits corresponding to specific energy level - this means that an electron cannot be found in the space between two orbits.

Since each orbit correspond to a a precise energy level, this means that the spectrum of emission and absorption of an atom is discrete. In fact:

- When an electron jumps from a lower energy level to a higher energy level, it absorbs a photon whose energy is equal to the difference in energy between the two levels - so photons of only specific frequencies are absorbed

- When an electron jumps from a higher energy level to a lower energy level, it emits a photon whose energy is equal to the difference in energy between the two levels - so photons of only specific frequencies are emitted

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.

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.