Question

Which equation to use to find out velocity of an object just prior to impact?

Answer 1

Use one of the formulae for constant acceleration. In this case, vf2 = vi2 + 2as, where vf is the final velocity, vi is the initial velocity (zero in this case), a is the acceleration (9.8 meters / second / squared), and s is the distance.

Answer 2

this is right but applied only when there is conservation of energy holds...in all other case u can apply conservation of momentum equation...