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Linear momentum conservation vs mecanical energy conservation

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jaumzaum
#1
Sep7-11, 09:06 PM
jaumzaum's Avatar
P: 248
A ball A (mass ma) with initial velocity v colides with a ball B (mb) initially stopped. A and B gets the same direction/velocity v', Calculate v'

By linear momentum conservation
ma.v = (ma + mb).v'
v' = mav(ma + mb)

But by mecanical energy conservation

ma.v/2 = (ma + mb).v'/2
v' = v (ma/(ma + mb))^(1/2), which is wrong

Why we can't use mecanical energy conservation, is there a energy dissipation?
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olivermsun
#2
Sep7-11, 09:32 PM
P: 641
Quote Quote by jaumzaum View Post
A ball A (mass ma) with initial velocity v colides with a ball B (mb) initially stopped. A and B gets the same direction/velocity v', Calculate v'
...
Why we can't use mecanical energy conservation, is there a energy dissipation?
Well, for A and B to get the same direction/velocity v' after the collision, don't they have to stick?

Does that sound like an elastic collision?


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