Question

Three trolley are free to move on a frictionless horizontal track. Trolley A has a mass of 2m and an initial speed 2v to the right; Trolley B has a mass of and an initial speed of v to the left; Trolley C has a mass of m and is originally at rest. All collisions are perfectly elastic.
The velocity of the center of mass of the system of the three trolleys after the last collision is
(1) 2v/3 (2) 3v/4 (3) 3v/2 (4) 3v/5 (5) v/3
Trolley B has a mass of ??
conserve momentum. It must start and end the same. So, that means
(2m)(2v)+(m)(-v)+(m)(0) = 4mv-mv = 3mv
since the final mass is 4m, that is 4m(3/4 v)

Looks Like #2.
Hey thank you very much:)

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