A heavy weight is dropped from a height of 1 m on a soda can, crushing it.
Is mechanical energy conserved in this process?
No. The potential energy decreases and the kinetic energy stays the same (zero before and after), so overall there's a loss of mechanical energy.
Is the total energy conserved in this process?
It has to! The lost mechanical energy has been transformed into other
forms of energy (heat, sound, etc.).