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# Re: [Phys-l] Action

For a simple high school level Action problem, see page 76, problem 15 at:
<http://www.sci-ed-ga.org/modules/driving/parts/StayingAlive.pdf>

Larry Woolf

I looked at this problem with interest.

But somehow I feel it's incomplete or at least unsatisfying in its present form. Surely a particle can take *any* of the four paths. For example, to take path B, start the particle moving at 10 m/s and provide a bumper that it runs into at the 1 m mark. I don't see anything wrong with that!

At minimum you've underspecified the constraints on the possible motions of the particle. If bumpers aren't allowed, what in the problem specifies that? If the particle can only start at certain speeds (apparently 1 m/s), what requires that? I think the problem needs to say that no external forces act on the particle between the instant after it starts until (hmm until what in fact? 10 seconds elapse? it reaches the 10 m mark? are we or are we not allowed to stop the particle when it reaches the 10 m mark?).

I understand the spirit of the problem. But how do we fix it up? Maybe we can't. With only KE involved, it seems to me path A may be the *only* allowed path once the problem is properly qualified, even without considering action at all.

Sorry to rain on a nice attempt to construct a high-school-level problem, Carl
--
Carl E Mungan, Assoc Prof of Physics 410-293-6680 (O) -3729 (F)
Naval Academy Stop 9c, 572C Holloway Rd, Annapolis MD 21402-1363
mailto:mungan@usna.edu http://usna.edu/Users/physics/mungan/