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Re: [Phys-l] coffee + cream (was: good questions)



On 10/10/2006 02:34 PM, Jim Krider wrote:
Hewitt has an overhead with this question on it.
Heat flow is proportional to delta T. If you wait to put the cream in
your coffee delta T is large for ten minutes allowing a fast flow of
heat. If you put the cream in right away delta T becomes smaller and
the amount of heat flow is much less for ten minutes.

Is that your final answer?

How much would you like to bet on the correctness/completeness
of that answer?

Hint: Before mixing, while the coffee is cooling down, the cream
is heating up.

If I get to choose the coffee-container and the cream-container,
and the initial temperatures, the answer given above might be
very, very wrong.

Jeffrey Schnick's experiment, while a step in the right direction,
does not cover all the bases. The original question is quite
underdetermined.

This *increases* the value of the question in my eyes. Real life is
full of ill-posed questions. Students do not get enough classroom
experience dealing with ill-posed questions. Not nearly enough.

http://www.av8n.com/physics/ill-posed.htm

=======================

Tangential remark:

If you want another example of a problem that is underdetermined, but
not obviously so, consider the "snapping the string" demo:

http://www.av8n.com/physics/ill-posed.htm#sec-string