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

[John Denker <jsd@av8n.com>]

On 05/05/2009 08:00 AM, LaMontagne, Bob wrote:
> What is "it's" in "it's obvious"? 

My bad.  I misread the question as

] Is my understandiing of the slingshot effect correct?
] ............................................ ^^^^^^^

whereas the actual question was
> Is my understandiing of the slingshot effect incorrect?

Therefore my short answer ("yes") was diametrically wrong.  
Sorry.

The longer answer remains correct.  I may not be able to
read, but I know a symmetry argument when I see one.

In the CM frame let the small object's initial velocity be 
V0.  Its final velocity is -V0.

The CM frame is moving relative to the lab at velocity U
which is (by hypothesis) collinear with V0. 

Therefore the small object's velocity goes from V=V0-U to
V=-V0-U.  This can be summarized by saying the speed |V|
increases by 2U (except when you do it the other way and
the speed decreases by 2U).

===================

It was a weird day yesterday.  I had been without sleep
since the morning of the previous day.  This is not a good
time to go the emergency room;  it's full of people who
don't have a primary care physician, or whose PCP isn't
available on the weekend, so the place is full of people 
who think they are dying of the flu.  They're not.

Later I was watering the flower garden and a 4 foot long
snake sauntered over to me.  He let me pick him up.  No
resistance.  Apparently he had been jumped by a jumping 
cactus.  I held him while my little niece tweezed out the 
cactus spines and applied antibiotic ointment.  Then we
let him go, and he sauntered away.