Can Energy Be Saved When Using an Air Pump to Lift a 5kg Weight?

[tiago000000]

Hi everyone! I regularly use the forum to learn but never registered to post anything, as I have nothing to teach really…
But today I have a question regarding the law of conservation of energy that I can’t find the answer to, and maybe someone will help me understand:

(I’ve attached a drawing)
Say we have a weight of 5kg at the bottom of a lake (11m deep), and an upside down 10L bucket above it attached to it by a few strings (9m deep). I then have an efficient air pump above the water line that pumps roughly 20L (I think, because of how it compresses down there) into the bucket and the whole apparatus comes up to the surface.

My question is: is the amount of energy used by the air pump equal/greater than the energy that would be needed to pull the same weight to the same place, or would it be possible for it to be smaller?

And if it was possible to use less energy to pump air down than it would be to pull the weight up, could you use this same principle to produce electric energy?

Ironically, as I’m waiting for the picture to upload, I’ve noticed a thread titled “why we don’t discuss perpetual motion machines”

Thank you everyone and I’m sorry for such a long post!

 

[berkeman]

Ironically, as I’m waiting for the picture to upload, I’ve noticed a thread titled “why we don’t discuss perpetual motion machines”

Yup.

And if it was possible to use less energy to pump air down than it would be to pull the weight up, could you use this same principle to produce electric energy?

Nope.

My question is: is the amount of energy used by the air pump equal/greater than the energy that would be needed to pull the same weight to the same place, or would it be possible for it to be smaller?

The energy to drive the pump will be equal to or greater than the change in gravitational potential energy (GPE) that the mass gained in being lifted to the surface.

As you noted, we don't discuss PMMs or over-unity mechanisms. Thread is closed for now.