work is done, it is equal to potential energy, which is equal to kinetic energy?

[waterbottlee]

hi!

can i say that
when work is done, it is equal to potential energy, which is equal to kinetic energy?

can somebody please correct me if i misunderstood it?

[OfficeShredder]

You completely misunderstand.

Conservation of energy essentially says that total mechanical energy is constant.

So suppose you have an object, and want to give it potential (gravitational) energy. For simplicity's sake, say it currently has a potential energy of zero. Then E_initial = E_final

But what is E_final? It's the potential energy you gave it minus the work done against gravity to lift the object. So you get mgh - f*d = 0

So in this case, you can consider the work done to be equal to the potential energy.

But now suppose you have an object that's moving down a ramp with friction. It has initial kinetic AND potential energy. It moves down the ramp at a distance d, which you can use trig to find the height h it has fallen. So again, E_initial = E_final. But E_initial = KE_initial + PE_initial, and E_final = KE_final + PE_final - f*d, where f is the force of friction. So in this case, you can't simply say that the work is equal to the change in one type of energy

[HallsofIvy]

Work done plus potential energy plus kinetic energy plus work lost through friction is a constant.