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甲乙两列火车相距为1000m,并分别以12m/s和8m/s的速度相向行驶.在两火车间有一个信鸽以22m/s的速率飞翔其间,当这只鸽子以22m/s的速率遇到火车甲开始,立即掉头飞向火车乙,遇到火车乙时又立即掉头飞向火车甲,如此往返飞行,当火车间距减小为零时,求:
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    He was the baby with no name. Found and taken from the north Atlantic 6 days after the sinking of the Titanic in 1912, his tiny body so moved the salvage (救援) workers that they called him “our baby.” In their home port of Halifax, Nova Scotia, people collected money for a headstone in front of the baby's grave (墓), carved with the words: “To the memory of an unknown child.” He has rested there ever since.

    But history has a way of uncovering its secrets. On Nov. 5, this year, three members of a family from Finland arrived at Halifax and laid fresh flowers at the grave. “This is our baby,” says Magda Schleifer, 68, a banker. She grew up hearing stories about a great-aunt named Maria Panula,42, who had sailed on the Titanic for America to be reunited with her husband. According to the information Mrs. Schleifer had gathered, Panula gave up her seat on a lifeboat to search for her five children -- including a 13-month-old boy named Eino from whom she had become separated during the final minutes of the crossing. "We thought they were all lost in the sea," says Schleifer.

    Now, using teeth and bone pieces taken from the baby's grave, scientists have compared the DNA from the Unknown Child with those collected from members of five families who lost relatives on the Titanic and never recovered the bodies. The result of the test points only to one possible person: young Eino. Now, the family sees no need for a new grave. "He belongs to the people of Halifax," says Schleifer, "They've taken care of him for 90 years."

    Adapted from People, November 25, 2002