Re: correct answer

[roger haar <haar@soliton.physics.arizona.edu>]

Hi  
	I think I see a flaw in this logic.  I think

		dx = v_ave dt = v/2 dt.  

Remeber the segment of hose is not moving before the force 
is applied and a time dt later is moving with velocity v.

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Thanks
roger haar U of AZ


On Thu, 9 Oct 1997, John Mallinckrodt wrote:

> 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
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