Magnetic Force and Work

[Sukuya]

Two long parallel wires carrying current I attract each other. Let's say we let them free to move then they will accelerate towards each other, thereby increasing the kinetic energy of the wires. But we know that magnetic forces can't do work on a system. Then how can magnetic force increase kinetic energy in this case.

 

[UltrafastPED]

It's the currents doing the work ... it's more obvious when you are lifting scrap metal with an electromagnet - then you can see the load on the generator.

You often need to do a careful analysis. See this old thread for a lengthy discussion:
https://www.physicsforums.com/showthread.php?t=229056