# How energy conservation is not violated here?

If I lift a book of mass $m$ from the ground and put it at height $h$,then initial and final energies with respect to ground are 0 and $mgh$ respectively.

So how energy is conserved here?

• don't forget that you yourself performed work when lifting up the book, your "internal energies" decreased. – Zoltan Zimboras Jan 26 '14 at 7:00
• internal energy is stored from the food we eat to be expended as we live and move. – anna v Jan 26 '14 at 7:10

you give your muscular energy to book, so when it is in air at $h$ height it is actually having energy $mgh$ given out by your muscles and if you drop that book, the potential energy inside that book will gets converted to kinetic energy slowly and will gain speed. Then the moment before when it reaches ground it has all the energy converted to kinetic energy and after that moment the energy gets transferred to earth. Hence conservation of energy is not violated.