A heavy weight is dropped from a height of 1 m on a soda can, crushing it.

Is mechanical energy conserved in this process?

1. Yes
2. No

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?

1. Yes
2. No

It has to! The lost mechanical energy has been transformed into other forms of energy (heat, sound, etc.).