a heavy box

[7bear]

When we lift a heavy box to a higher position, energy from our bodies(chemical energy) is lost and there is energy gain(potential energy) in the box.

After, when we release the box from that position to the original one(lower position), there is P.E. lost in the box. So where does lost energy go?
We gain energy from the box!? I think it is impossible....... :eek:

[Integral]

The human body is not a simple physical system so you cannot treat as one. The human body expends energy to either raise or lower the box, in either case the work required is the same. If you were to simply push the box off the shelf it would hit the ground with a velocity determined by the height of the shelf, when you lower the box you are applying a force which counters gravitational forces to reduce the speed with which it hits the ground. Unfortunately your body does not have a mechanism for storing the lost energy of the box.

[russ_watters]

If you simply drop the box, the energy goes into sound, heat, and deformation of the box when it hits the ground.

[jcsd]

The answer is that the energy is still present (ignoring any possible loses) in the box as the box's kinetic energy. If we wish to bring the box to rest at the orginal lower postion the only way to achieve this is is to transfer the kinetic energy of the box to some other part of the system.

[Nenad]

If you simply drop the box, the energy goes into sound, heat, and deformation of the box when it hits the ground.

this is the right answer.

[jcsd]

this is the right answer.
Well it depnds if the box does hit the ground.

[Nenad]

assuming gravity is present.