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Re: [Phys-l] rich context luncheon meat




Of course, after considering all that, it occurs to me that the wires
better be able to hold the performer's full weight momentarily just
as the fall starts. Perhaps the problem is fatally flawed after all.


Couldn't you fix the fatal flaw by introducing some sort of pin that is
pulled to start the fall? I think students can look beyond that part.
Anything more complicated really does involve looking at tension in a more
detailed way (stress tensor) and is probably not a good use of time in
intro-physics.

I think the problem sounds pretty good, but it's a bit of a risk to expect
the students to realize that you need two wires to support Peter's weight as
he falls. Personally, I'm not sure I would say that myself. It's more
tempting to just say "well, the wire can only support 70 lbs, so you can't
do it." Perhaps in setting up the problem, I would include Peter's weight
to make it more defined (it makes sense that they have the role cast if
you're building this rig). Another option is the "failure is not an option"
clause: don't allow students the option of saying "this is impossible," but
rather state that it is indeed possible and they have to make it work.
Maybe even include that multiple wires can indeed be used. The hint can be
as subtle as saying that you have access to as many pulleys as you need.

I like the fact that you want students to use up the piano wire where it is
in view of the audience, necessitating the second type of wire on the ramp.
I think the process of joining those two types of wire would be a bit of a
hangup for some students, but not so much that I'd change it.

One last thing - with these results: mg = 71lb, a = .91g, t = 1.5s, T =
51lb, Peter hits the ground at over 13 m/s (30 mph). That's pretty much
leg-breaking. I'm not sure what kind of talent they have at the Playmakers'
Theatre (are the actors professional stuntmen?), but I'd make sure that
Peter had something soft to land on.

Make sure to post results after you finally hand this one to your students!