I am confused if I put a book from ground to a table at height 'h' ,note that the book is at rest before and after putting , total work done on book is 0, as change in k.e. Is 0 ,therefore total transfer of energy on book should also be 0 but after putting the book on the table at height 'h' the book gain a p.e. Of 'mgh'.how?

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anonymous · Answer

And is this in the right place?????? Or should it be in math?

anonymous · Answer

And if you've got an answer, PLEASE REPLY!!!! If its too confusing please let me know.

anonymous · Answer

Yes, you are confused! The idea of a potential energy function is that it keeps track automatically of the work done by a force always present in a particular problem. The gravitational potential energy represents the work done by the weight mg of an object. So, if you use potential energy, you do not count the work weight does, that is ΔK+ΔU=Wext where Wext is the work done by all forces other than gravity, in your example that is you. So, to lift the book you must exert a force upward of magnitude mg for a distance h and so the work you do is Wext=mgh; since kinetic energy has not changed, ΔU=mgh.

anonymous · Answer

Ok thank you so much @JustKillTheNoise

anonymous · Answer

Oh you're welcome @Magic87

anonymous · Answer

Aw you gave me a medal too?? Aw, you just broke my heart Kill. lol

anonymous · Answer

Sorry!:(