My friend asked me-
Imagine that we pull up a pen which is initially at the ground slowly upwards.At a certain point we see that its total energy is due to its P.E.So,how can we say total energy is constant?
My thinking is that it does gain some P.E. at that height but as gravity is a conservative force it will regains its previous energy once we put it down to the previous level.Hence the total summation of energy is 0 when we return to the starting position.
Is this explanation correct?
Thanks for your opinion.