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# M1 momentum watch

1. Can someone please explain how you know which particle in the below question has velocity v and (v+1).
Thank you
2. I think....(there's probably a mathematical proof for this)

Given that they're going in opp directions to start with, and the 3kg one clearly has greater momentum, then after the colliison the momentum will be in this direction, ie they'l both now be moving in the direction the 3kg was going.

So, on that basis, the small one must be going faster because the big one can't get past it. So I'd put the 3kg one at v and the 2kg one at v+1

If in any doubt, try it both ways, you will find that only one gives you the same momentum change for both particles.
3. (Original post by phys981)
I think....(there's probably a mathematical proof for this)

Given that they're going in opp directions to start with, and the 3kg one clearly has greater momentum, then after the colliison the momentum will be in this direction, ie they'l both now be moving in the direction the 3kg was going.

So, on that basis, the small one must be going faster because the big one can't get past it. So I'd put the 3kg one at v and the 2kg one at v+1

If in any doubt, try it both ways, you will find that only one gives you the same momentum change for both particles.
Thank you. That makes sense. I worked out which one it would be from the fact that the impulses would have to be equal but I knew I was missing some common sense like the fact that they didn't pass😅

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