Question

where we use the first equation of the motion, second equation of the motion and third equation of the motion and also give examples

Answer 1

v = v0 + at 

This is the first equation of motion. It's written like a polynomial — a constant term (v0) followed by a first order term (at). Since the highest order is 1, it's more correct to call it a linear function.

s = s0 + v0t + ½at2 
This is the second equation of motion. It's written like a polynomial — a constant term (s0), followed by a first order term (v0t ), followed by a second order term (½at2). Since the highest order is 2, it's more correct to call it a quadratic.

v2 = v02 + 2a(s − s0) 
This is the third equation of motion. Once again, the symbol s0 [ess nought] is the initial position and s is the position some time t later. If you prefer, you may write the equation using ∆s — the change in position or the displacement.