Conceptual doubt on motion of quantum particles My sir told me to apply realitvistic mechanics on motion of electron but in some question he also used kinematical equations say for example calculating time required in reaching from some point in space to another point in freespace. Are the kinematical equations universal for every motion of every object?
 A: There are specific rules for when one can use quantum mechanics and one can use classical mechanics equations even for elementary particles.
It all depends on whether in the dynamical variables of the problem the value of h, Planck's constant, which controls the Heisenberg uncertainty relations,  can be assumed to be zero, or the calculation involves quantities where h has to be taken into account.
The path of a free electron can be calculated classically as long as there are no large momentum and energy transfer interactions on its path. That is how beams of particles are calculated  in accelerators and colliders. In event analysis of interactions, the tracks of outgoing particles are fitted with classical solutions in the magnetic fields of the detectors. On this bubble chamber event, the first famous Omega minus detection


The bubble chamber picture of the first omega-minus. An incoming K- meson interacts with a proton in the liquid hydrogen of the bubble chamber and produces an omega-minus, a K- and a K+ meson which all decay into other particles. Neutral particles which produce no tracks in the chamber are shown by dashed lines. The presence and properties of the neutral particles are established by analysis of the tracks of their charged decay products and application of the laws of conservation of mass and energy.

The momenta of the tracks are fitted using the motion of charged particles in the magnetic field (perpendicular to the picture) of the chamber.
