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M2 collisions question with kinetic energy- edexcel watch

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    Hi, I am having trouble with the following problem (small detail of the problem):
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    I understand the general argument and am confident I could set up such an argument myself. The problem I am having though concerns the marked area below:

    So these to possible velocities for A and B have been found. Clearly only one velocity is possible and the solution says that y>x ( i.e. the speed of the 2kg sphere is greater than the speed of the 1kg sphere). But why is y>x?

    Thanks for any help!
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    http://pmt.physicsandmathstutor.com/...hapter%204.pdf
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    It's a bit early in the morning for me but is it just that sphere A is behind sphere B so can't possibly be going faster (because it would then have to overtake B in some way or would push it along and they'd both move at the same speed)?
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    (Original post by phys981)
    It's a bit early in the morning for me but is it just that sphere A is behind sphere B so can't possibly be going faster (because it would then have to overtake B in some way or would push it along and they'd both move at the same speed)?
    Thanks for your reply! I don't think that works in this case though...
    I can't see that the question implies that A is behind B or that A and B can't collide a second time.
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    I can't see how it can NOT be behind B. They are in a line, right? How could it get past B?
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    here it is in a previous life https://www.thestudentroom.co.uk/sho....php?t=2302563
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    (Original post by phys981)
    I can't see how it can NOT be behind B. They are in a line, right? How could it get past B?
    Isn't it possible that they collide a second time? ( I do see that this is a bit absurd as they would have to collide instantaneously, after the first collision...)
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    They can only collide again if they'd actually lost contact - which they won't do if, as you suggest, A is going faster than B.
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    (Original post by phys981)
    They can only collide again if they'd actually lost contact - which they won't do if, as you suggest, A is going faster than B.
    Oh right! Makes sense... Thanks a lot for your help and patience.
 
 
 
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