What will happen without this theory of bohr's second postulate?

Linear momentum refers to the motion in a straight line, from one point to another. And angular momentum is the rotational equivalent of linear momentum. Since the electrons move in circular tracks or orbitals, the angular momentum is used to calculate the movement of these electrons.

This theory simply stated that there exist stationary orbits around the nucleus in which electrons rotate without dissipating any type of energy. And if the electrons try to change their orbits, then there will be a gain or loss of energy depending on the situation.