题干

某同学通过以下步骤测出了从一定高度落下的排球对地面的冲击力:将一张白纸铺在水平地面上,把排球在水里弄湿,然后让排球从规定的高度自由落下,并在白纸上留下球的水印.再将印有水印的白纸铺在台秤上,将球放在纸上的水印中心,缓慢地向下压球,使排球与纸接触部分逐渐发生形变直至刚好遮住水印,记下此时台秤的示数即为冲击力的最大值.下列物理学习或研究中用到的方法与该同学的方法相同的是

A:建立“合力与分力”的概念

B:建立“点电荷”的概念

C:建立“瞬时速度”的概念

D:研究加速度与合力、质量的关系

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答案(点此获取答案解析)

A

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根据短文内容,选择最佳答案。

    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