TITLE: What happens to the kinetic energy of a dropped ball when it comes to rest on the ground?
QUESTION [1 upvotes]: If we want to drop a ball from a height, we calculated that potential energy at bottom is zero and we say it is converted into kinetic energy. At that movement, if it is a kind of sand, we find it will be at rest. So, what happened to its mechanical energy over there?

REPLY [0 votes]: A better question in this case is to ask if we drop a feather from a height, we see that the feather settles on the ground quietly. I you can under this which is a lot easier to explain and much mor intuitive. 
So as any object falls in a fluid (in this case air) it firstly accelerates and finally reaches constant velocity termed as terminal velocity, at this time the gravitational force equals the viscous force (applied by air). For feather the terminal velocity is very less and all the way down the potential energy is dissipated as heat and sound. 
PS: You should read about terminal velocity and the variable it depends on in much more detail to have a more clear understanding.
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