1. The problem statement, all variables and given/known data This is elementary level stuff and I am pretty much past this, and yet I can't seem to find a suitable way of explaining this.I was thinking about Potential Energy of a particle of mass m falling freely under gravity(ignoring air resistance, again, beginner stuff :P) from a point A 10m above a point B which is on horizontal ground, vertically below A.GPE at A is 10mg.At ground level all GPE=KE so KE=10mg.That was scenario 1, but the 2nd scenario is a bit different;lets say that the instant the particle reaches point B(just before actually touching but theoretically there-sounds weird I admit :/) the ground(or in this case, point B) drops by 10 meters.Now, GPE at A is again 10mg(remember the ground was there when it was first let go)again all GPE=KE so KE=10mg but since it drops further 10 meters so KE actually becomes 20mg! 2. Relevant equations K.E=1/2mv2 P.E=mgh 3. The attempt at a solution I tried saying that it all depends on the point from which we take the height as standard and that this isn't always at sea level.I have even included a diagram to help u better understand the situation if I happen to sound confusing.