That's not where cracker came from. You have never read in a slave journal the term cracker, in fact the word cracker wasn't even introduced into the english language until the late 1800s well after slavery.
cracker comes from being flavorless, stale, pale and lame. You are literally the human version of the food.
crack of the whip is something cacs created to try to feel good about the slang but no. Most black people know the term isn't from 'crack of the whip'. No one uses the term crack for a whip sound, not then, not now, never ever in the history of english. It's not even my first language and even I know this