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Re: [Phys-l] Conservation of energy in nuclear reactions



What is "it's" in "it's obvious"? The symmetry argument in the center-of-mass frame is what immediately gives you that an elastic collision between a small object initially at rest and a very massive object moving at speed V will result in a final speed for the small object of 2V. The speed of the small ball in the CM is -MV/(M+m) - the sign reverses after the collision - add the speed of the CM which is MV/(M+m) - get 2MV/(M+v) - reduces to 2V. Using gravity or the Couomb force instead of actual contact in the collision is what I always thought was the meaning of the term 'Slingshot effect'.

I'll look at Carl's Eqn(3) again with a little more thought after I finish grading a final. I'm probably misinterpreting it - didn't mean to derail the thread.

Bob at PC

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker [jsd@av8n.com]
Sent: Monday, May 04, 2009 6:48 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Conservation of energy in nuclear reactions

On 05/04/2009 02:57 PM, LaMontagne, Bob wrote:
If the interaction occurs such that it is almost one dimensional, the
lighter object should pick up twice the speed of the much heavier
object. That is the essence of my understanding of the slingshot
effect. ...

To the group: Is my understandiing of the slingshot effect incorrect?

Yes.

In the center-of-mass frame, it's obvious by symmetry.

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