Re: correct answer

["Steven T. Ratliff" <str@nwc.edu>]

On Oct. 9, Mark Shapiro wrote:
> 	In preparing for class today I was reviewing some problems in
> Halliday, Resnick and Walker (5th ed) - Chapter 7.  I believe the answer
> to problem 15E on page 150 is incorrect.
>
> 	The problem states that a 12 m long firehose is uncoiled by
> pulling the nozzle end horizontally along a frictionless surface at the
> steady speed of 2.3 m/s.  The mass/length of the hose is 0.25kg/m.  How
> much work has been done on the hose by the applied force when the entire
> hose is moving?

An interesting comment on this.  In the fourth edition, the problem 
is on p. 184 (problem 27E).  Everything is much the same except the 
statement of the problem to be solved:  "How much kinetic energy is 
imparted in uncoiling 12 m of hose?"

This makes the problem easier, and the answer is certainly correct in 
this case (with the obvious reasonable assumptions).

Sincerely,
Steven Ratliff




Steven T. Ratliff
Associate Professor of Physics
Northwestern College
3003 Snelling Av. N.
Saint Paul, MN  55113-1598

Internet:  stratliff@nwc.edu (or str@nwc.edu)