I seldom try to "advertise" a paper on arXiv that is yet to be published, but I just found this a fascinating read and an amusing one as well.
The authors of this preprint are trying to show how an analysis in Halliday and Resnick on why 2 sheep can survive a violent head-butting without suffering any brain injury is not actually correct. The subject matter is rather amusing (at least to me), but there's some rather good basic mechanics issue here being presented, especially for motion without the assumption of a constant acceleration. So I think any physics undergraduate that have had sufficient calculus can follow this.
Now, anyone willing to read it carefully enough to see if they've done the physics correctly? :)