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Jul31-11, 10:07 AM
The work-energy theorem in this case tells me that the net work done on the body is zero since there is no change in kinetic energy. Does this mean that that total energy of the body remains constant. But surely it has lost some energy since it is closer to the surface than before.
When a body is lets say, kept on a table, it does not move from its position relative to the surface due to an opposite force exerted by the table on the body equal to its weight. We say that it possesses potential energy with reference to the surface. And this remains constant because its height remains constant. Another way to tell this is that the net work done on it is zero. (Am I right?)
But in my original situation it is the same case isn't it? Except that now the body now has some initial velocity. But potential energy changes even though net work is zero.
It seems you are confused about the concept of potential energy. I wrote this:
The point is that when we say an object has potential energy, this energy is not property of the body, but a property of the body being in an external force field that exerts a force on it and does work on any trajectory that is simply equal to the difference of the potential energy between the initial and final positions.