What is a word that is a feeling/emotion of releasing pent up anger against an inanimate object
Solution 1:
I suggest "catharthis", though the dictionary definition is more focused on expressing the emotion through art
Dictionary.com describes it as:
The purging of the emotions or relieving of emotional tensions
Another definition from Merriam-Webster
the act or process of releasing a strong emotion (such as pity or fear) especially by expressing it in an art form
You would say "ahh, that was cathartic"
Edit: you might also say "ahh, that was freeing", as in you've been freed from your emotions of anger and stress. Less powerful, but perhaps more accessible.