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Re: Crocodiles problem.



Serway and Beicher, 5th edition has the same problem, in which it is stated that "Jane, whose mass is 50.0 kg, needs to swing across a river (having width D) filled with man-eating crocodiles..."

Clearly Jane has nothing to worry about.


At 11:11 AM 10/18/01 -0700, you wrote:
Would those who have College Physics (5th edition) of Serway
and Faughn agree that problem 5.63 (on page 147) is puzzling?
It starts with “Jane, whose mass is 50 kg, needs to swing
across a river filled with man-eating crocodiles in order
to save Tarzan from danger. ….”

The picture shows that her initial elevation is higher than
that of Tarzan but the difference of elevations is not given.
Is it not true that the answer to question (a) depends on
the difference of elevations?

I see how the problem is solved in the Instructor’s manual
but I am not convinced that the answer should not depend on
the difference of elevations. The hint given to students is:

“First determine the potential energy associated with the
wind force. Because the wind force is constant, use the
analogy with the constant gravitational force.”

The solution shown in the Instructor’s Manual does follow
the hint. Is it correct to associate a potential with the
air resistance force?
Ludwik Kowalski