题干

如图所示,固定于水平面上的光滑斜面足够长,一轻质弹簧的一端与固定在斜面上的木板P相连,另一端与盒子A相连,A内放有光滑球B,B恰与盒子前、后壁接触,现沿斜面向下的力推A使弹簧处于压缩状态,然后由静止释放,则从释放盒子A直至其获得最大速度的过程中,下列说法正确的是(   )

A:弹簧的弹性势能一直减小到为零

B:A对B做的功等于B机械能的增加量

C:弹簧弹性势能的减小量等于A的机械能的增加量

D:A所受重力和弹簧弹力做功的代数和等于A的动能的增加量

上一题 下一题 0.0难度 选择题 更新时间:2015-03-18 09:06:37

答案(点此获取答案解析)

B

同类题1

Roald Dahl was one of the most successful writers of children's books. He sold millions of books all over the world. Many of his books have been made into films and videos. He is so famous that there is even a Roald Dahl Museum you can visit.

Roald Dahl was born in 1916 in Wales, Britain. His father was rich but he died when Roald was very young. Roald and his mother lived a hard life. He had to leave school and went to Africa where he worked for an oil company.

    In 1939 Roald became a pilot, but he had a bad accident. It made him limp(瘸的) for the rest of his life. After this, Roald went to America where he wrote a story about his experience as a pilot. It was so good that it was put in a magazine.

       Roald married an American film star. They bought a house in England and had five children. From 1960 to 1965,    ▲   : Theo, one of his children, was hit by a taxi and was seriously hurt. Olivia, one of Roald’s daughters, died of a strange illness. Soon after this, his wife also had a serious illness. It took her years to get completely better.

 Gradually Roald became more and more successful. He always did his writing in an old shed(棚) at the back of his house. He always sat in the same old armchair with a wooden board on his lap.

 “One of the nice things about being a writer,” he once said, “is that all you need is what you’ve got in your head and a pencil and a bit of paper.”

       In 1983 Roald wona big prize for his book The BFG. During his life, Roald wrote many famous books, such as Charlie and the Chocolate Factory, Matilda, Fantastic Mr. Fox

       After he died in 1990, Roald left money to help people with serious illnesses and those with problems with reading and writing.