Answer:
M1 v1 + M2 v2 = M1 V1 + M2 V2
Assuming we are to fine V2 (the problem is not clear on this point)
50 * 5 + 100 * 10 = 50 * 8 + 100 V2 conservation of momentum
V2 = (250 + 1000 - 400) / 100 = 850 / 100 = 8.5 m/s
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