题干

如图(甲)所示,质量不计的弹簧竖直固定在水平面上,t=0时刻,将一金属小球从弹簧正上方某一高度处由静止释放,小球落到弹簧上压缩弹簧到最低点,然后又被弹起离开弹簧,上升到一定高度后再下落,如此反复。通过安装在弹簧下端的压力传感器,测出这一过程弹簧弹力F随时间t变化的图像如图(乙)所示,则

A:时刻小球动能最大

B:时刻小球动能最大

C:~这段时间内,小球的动能先增加后减少

D:~这段时间内,小球增加的动能等于弹簧减少的弹性势能

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C

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    Birthdays often involve surprises. But this year's surprise on the birthday of the great British playwright William Shakespeare is surely one of the most dramatic.

    On April 22, one day before his 441st birthday anniversary, experts discovered that one of the most recognizable portraits of William Shakespeare is a fake. This means that we no longer have a good idea of what Shakespeare looked like. “It's very possible that many pictures of Shakespeare might be unreliable because many of them are copies of this one,” said an expert from Britain's National Portrait Gallery.

    The discovery comes after four months of testing using X-rays, ultraviolet light, microphotography and paint samples. The experts from the gallery say the image —commonly known as the “Flower portrait”— was actually painted in the 1800s, about two centuries after Shakespeare's death. The art experts who work at the gallery say they also used modern chemistry technology to check the paint on the picture. These checks found traces of paint dating from about 1814. Shakespeare died in 1616, and the date that appears on the portrait is 1609.

    “We now think the portrait dates back to around 1818 to 1840. This was when there was a renewed interest in Shakespeare's plays,” Tarnya Cooper, the gallery's curator (馆长), told the Associated President.

    The fake picture has often been used as a cover for collections of his plays. It is called the Flower portrait because one of its owners, Desmond Flower, gave it to the Royal Shakespeare Company.

    “There have always been questions about the painting,” said David Howells, curator for the Royal Shakespeare Company. “Now we know the truth, we can put the image in its proper place in the history of Shakespearean portraiture.”

    Two other images of Shakespeare, are also being studied as part of the investigation and the results will come out later this month.________