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Don't be fooled!! In each of the four situations, the two carts involved in the impulse encounter the same impulse causing the same momentum change which results in the same final momentum. Differences in mass will only effect the resulting velocity change. And if Team A "pushes on" Team B's cart, then there is an equal and opposite reaction force exerted by Team B's cart upon the legs of the Team A "pusher". So there is never any situation in the given four in which one of the teams encounters a greater momentum.