[Phys-L] Re: Ambiguous Question

[David Schuster <david.schuster@WMICH.EDU>]

1.  Besides the wording ambiguity issue that Mike Edmiston raised, I found
myself thinking about the role of the WATER in this problem. And what effect
it would have on the answer.

2.  Sure, water is not very resistive in this case, but.. if we start
thinking a bit toward a more extreme case (toward mud?!), the 17m answer
starts looking better and better..for other reasons of course.

David Schuster
Physics Department and Mallinson Institute for Science Education
Western Michigan University, Kalamazoo, MI 49008-5252, USA.
Tel: +1 (269) 387-5844 Work     Fax: +1 (269) 387-4998 Fax
Tel Home: +1 (269) 345-1412
Email:  david.schuster@wmich.edu
--

Mike Edmiston wrote in part:
> I have been asked to comment on a question on an exam at some other
> university that I will not mention.
>
> On an exam, the professor intended to write a center-of-mass problem
> similar to what we often see...
>
> A 20-kg dog is in a 50-kg boat on a calm lake.  The boat is
> free-floating without any anchor or attachment to the dock.  The dog 20
> m from the dock.
>
> Here is the ambiguous statement followed by the question...
>
> The dog walks 3 meters toward the dock.  After this walk, how far is the
> dog from the dock?
>
> Here's why it is ambiguous... The professor did not say with relation to
> what the dog moved.  Did he travel 3 meters relative to the dock, or
> three meters relative to the boat.
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