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Re: test problem



-----Original Message-----
From: Justin Parke [mailto:FIZIX29@AOL.COM]
Sent: Wednesday, December 05, 2001 12:18 PM

[snip]

"This question is related to the conservation of energy lab:
a 3.0 kg mass is hung from a spring which is then observed to
stretch 15 cm. The mass is then pulled down to 25 cm from
the unstretched length of the spring and released from rest.
a) find the spring constant of the spring
b) find the total potential energy (spring and
gravitational) of the system after it is stretched down.
(Define the origin to be the bottom of the unstretched spring.)
c) Use conservation of energy to find the speed of the
mass as it passes through the 15 cm point"

[snip]

I am beginning to wonder if I have no understanding of
mechanical energy because when I work the problem this way I
obtain a negative kinetic energy. This is the same
difficulty the students had in my first email.

From your previous e-mail:

These diligent students found that the total potential energy
was greater at the midpoint than at the top, which would lead
to negative kinetic energy.

Can you show us your calculations?

--------------------------------------------
Robert Cohen rcohen@po-box.esu.edu
570-422-3428 http://www.esu.edu/~bbq
Department of Physics
East Stroudsburg University
East Stroudsburg, PA 18301
--------------------------------------------