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# momentum help! watch

1. hi stuck on this question
Two spheres A and B of equal radii and masses mkg and 2mkg respectively are moving in the same direction along a straight line. A has speed kums-1 (k>1) and B has speed ums-1. After A hits B it is brought to rest. The coefficiet of restitution between A and B is e.
a) show that e = k+2 / 2(k-1
b) deduce that k >_ 4
2. (Original post by xosarcycowxo)
hi stuck on this question
Two spheres A and B of equal radii and masses mkg and 2mkg respectively are moving in the same direction along a straight line. A has speed kums-1 (k>1) and B has speed ums-1. After A hits B it is brought to rest. The coefficiet of restitution between A and B is e.
a) show that e = k+2 / 2(k-1
b) deduce that k >_ 4
Have you done any working? Draw a diagram, and write out what e is in terms of the velocities before and after.
3. think i've done it but not sure =/ lol
4. (Original post by xosarcycowxo)
think i've done it but not sure =/ lol
It's two "show that"s - it should be fairly obvious if you've done it :P
5. i know that but I start making it fit whether it does or not lol just to try and get the right outcome
6. I'm also stuck on this, no idea where the 2's and brackets are coming from.
7. (Original post by xosarcycowxo)
i know that but I start making it fit whether it does or not lol just to try and get the right outcome
Post what you've done so far - help us to help you
8. (Original post by tommm)
Post what you've done so far - help us to help you
I did the following.

m1u1+m2u2 = m1v1+m2v2

(m * ku) + (2m * u) = (m * 0) + (2m * v2)

m1v1 cancel out because of a multiple of 0 so then the equation becomes.

(m * ku) + (2m * u) / 2m = v2

I'm not sure where to go from here because of moving terms about.
9. (Original post by ThrashMetal)
(m * ku) + (2m * u) / 2m = v2
I'm not sure where to go from here because of moving terms about.
Your bracket's a bit off - after dividing by 2m, you should get:
.
Now, what is ?

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