Beating a dead horse =>
It may be worth pointing out a more general result:
Note that the result equations (1): U2=v1 and (2): v2= 0
follow from only m=M, even without taking any limit.
These are well known results for any one dimensional, elastic
collision between equal masses, without any mention of
immovable or unstoppable.
From: Bob Sciamanda
Sent: Wednesday, February 23, 2011 10:29 AM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] (no subject)
A possible specific embodiment of this conundrum:
Consider a one dimensional, elastic collision between m and M, in the
(initial) rest frame of M.
Let v1,v2 be the initial and final velocities of m. The initial and final
velocities of M are 0 and U2.
From momentum & kinetic energy conservation, one routinely obtains:
(1): U2 = 2*v1/(1+M/m) , and
(2): v2 = v1(m-M)/(m+M) .
To mimic the specs of your conundrum,
let m = M and take the limit as m (=M) goes to infinity.
This gives:
(1): U2 => v1 , and
(2): v2 => 0
m and M simply exchange velocities.
From: Connie tial
Sent: Wednesday, February 23, 2011 9:26 AM
To: phys-l@carnot.physics.buffalo.edu
Subject: [Phys-l] (no subject)
A student posed the following question: What would happen if a
theoretically unstoppable object collides with a theoretically unmovable
object? He predicts everything...the world...would end. I know the world
will not end...what is the opinion of this group?
Connie L Tyree
Physics/Chemistry/Earth & Space Science Teacher
BS Comprehensive Science; BGSU
MAT Physics; BGSU
Seneca East High School
13343 E US 224
Attica, OH 44807
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