Here's one I liked:
I was told to set my clock back an hour when it showed 2AM on November 1st. I've done this 8 times now. When can I stop setting the clock back?November 2nd of course. You'd think those directions were complicated or something. Let's try basic physics:
Q: A frictionless elephant with a mean diameter of 10 ft jumps off the top of a 600 ft tall building. His time to first contact with the ground is left to the student since it always is. For extra credit, what do we call the brief moment between the elephants first contact with the sidewalk and the final flattening of his top surface?
A; The Moment of Inertia of course.
So I didn't make it as a professional comedian. Let's see you do better.