Often when a word problem refers to an "object" or a "particle" moving through the coordinate planes, I decide on an identifiable object or particle to use in my problem. In this case, I was hungry and chose to use watermelons.

Some people find it amusing that I only partially substitute objects problems, i.e. "I'm standing on the x-axis" or "a watermelon moving around the origin" instead of supplying a real identity for the axes or the origin.

I like it better that way.