What does the symbol "e3" represent?

E₃ = energy in third energy level.

Explanation:

The energy of an electron is third orbit is given by :

Where

Z is the atomic number

n is principal quantum number and n = 1,2,3....

i.e. the energy of an electron is inversely proportional to the principal quantum number.

E₁,E₂,E₃.......... shows the energy of an electron in first, second and third energy level respectively.

the bal will not change its velocity.

pythagoras' theorem

square root (-5^2+9^2)

square root (25+81)

square root (106)

angle is tan^-1(9/5)

neg x, pos y