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**[SOLVED] Momentum problem**

Two astronauts float in space, at rest relative to each other. The first astronaut, mass 63.4 kg, holds a ball of mass 7.28 kg, which she throws at speed 6.17 m/s. The second astronaut, mass 83.1 kg, then catches the ball. Find the speed one astronaut is moving relative to the other after one throw and one catch.

P = mv

M1V1 + M2V2 = M1Vf + M2Vf

I found the momentum of the first astronaut throwing the ball which is:

7.28(6.12) = 63.4 vf

7.28(6.12)/63.4 = vf

-.7027 m/s = vf

Also the momentum of the second astronaut catching the ball:

83.1(0) + 7.28(6.17)/ 83.1 + 7.28 = vf

.497 m/s = vf

but im rather confused about what its asking for. It asking for the speed one astronaut is moving relative to the other. Does it matter which astronaut's speed I use or do I need to use a relative velocity equation?

If I need to use a relative velocity equation would it be something like:

V astro b relative to a = V astro a relative to b + V of astro A and B