First Barbie Bungee...now Zipline with Polly Pocket

So excited about an activity I'm in the middle of planning.  We are starting 8.G.B.6, 8.G.B.7 and 8.G.B.8- all about understanding and applying the Pythagorean Theorem. In particular, I was trying to figure out how I might approach 8.G.B.7, which says: Apply the Pythagorean Theorem to determine unknown side lengths in right triangles in real-world and mathematical problems in two and three dimensions.  I've done a lot in middle school math with Pythagorean Theorem before, but never really in three dimensions.

Here's what I'm thinking...I really like the Barbie Bungee problem that a variety of tweeters and bloggers were using a little while back.  We're going to try creating the longest possible zipline in our classroom.   My daughter and husband went ziplining in the Caribbean so I was thinking of using a short video from that as the intro.  I think I'll grab several big boxes from here and there so that each group of students can have a box.  Hopefully they will want to design the longest possible zipline in their box...they will have to calculate how long of a piece of string they will need to create their zipline.    Then everyone will figure out how long of a zipline we could make in our classroom.

Not related to the Pythagorean theorem, but an interesting question of acceleration...does the longest zipline make for the fastest ride?  Some of the boxes will result in a steeper zipline...might make for some fun data collection and extension problems.

Any thoughts on other ideas with this?