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Re: oscillations test question



On Wed, 20 Nov 2002 14:16:14 -0500 "Carl E. Mungan" <mungan@USNA.EDU>
writes:
I'm interested in hearing what folks think of the following question
in the test bank for Giancoli:

I'm not sure if Carl is being serious or if he expects non-conventional
responses to his question. However, let us assume that he is serious
and give him the benefit of doubt in this case.

When a spring is stretched, its potential energy increases regardless of
whether the spring is on the earth or in space.Although the system may
be in a stable equilibrium with respect to it's surroundings, there may
sources of potential energy within the system that appear upon release
of restraining forces.

The change in gravitational energy over a vertical distance of a meter or
two is very close to zero. If we were to consider such small changes in
gravitational potential energy, we must also consider the small changes
in the non-uniformity of the spring, the increase in the air pressure at
lower altitudes, and the heat that is generated and radiated as the the
spring is stretched.

Herb Gottlieb from New York City
(Where our engineers have calculated that the decrease in gravitational
force over a vertical distance of a meter is less than the weight of an
rch)

Chap 14 #11. Two hundred grams hung on a spring stretches it 8.4
cm. How much energy is stored when stretched 8.4 cm?

Before reading the rest, decide how you would answer this and why.

While a number of answers are possible, the most reasonable answer
in my mind is zero. By definition, a system at rest in stable
equilibrium is at a potential minimum.

The purported answer of 82 mJ only considers the increase in the
elastic potential energy and neglects the decrease in the
gravitational potential energy.

It is true that no zero points are specified. This is why I can
only say my answer is reasonable, and other interpretations are
possible.
Comments?
--
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu http://physics.usna.edu/physics/faculty/mungan/

This posting is the position of the writer, not that of SUNY-BSC,
NAU or the AAPT.



This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.