Heat seems like the easy answer, but interparticle collisions should decrease as the ball slows.
And what is the question?
Oh dear! I copy pasted the question. The question is this:
If I throw an iron ball at a magnet, the ball will bounce off of the magnet, but be slowed by its attraction to the magnet. Since energy cannot be created or destroyed, where does the original kinetic energy go?
What about the attraction as the ball approaches the magnet? If you are going to account for the attraction as the two are separating, you need to account for it as the two are approaching as well.
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