Re: correct answer

[John Mallinckrodt <ajmallinckro@CSUPomona.Edu>]

On Thu, 9 Oct 1997, Martha Takats wrote:

> Mark, if your answer is right, what happened to the other half of the
> energy? Dissipative forces inside the uncoiling hose?

I think this must be the case.  The force F = (dm/dt)v acting on each
element of mass dm over a distance dx = v*dt would give each element an
energy of (dm)v^2 and, therefore a velocity of v*sqrt(2) unless
dissipative forces came into play.  In effect, each element gets jerked
into motion with an impulse greater than what is necessary to achieve the
final velocity.  The excess work causes an increase in the internal
energy. 

Thus, I think Mark is right and the book is wrong.

John
-----------------------------------------------------------------
 A. John Mallinckrodt      http://www.intranet.csupomona.edu/~ajm
 Professor of Physics    mailto:ajmallinckro@csupomona.edu
 Physics Department       voice:909-869-4054
 Cal Poly Pomona            fax:909-869-5090
 Pomona, CA 91768-4031   office:Building 8, Room 223