如图所示，用一根长绳，把它的上端固定在天花板上，下端拴一小球_爱下问搜题

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问题问答题

如图所示，用一根长绳，把它的上端固定在天花板上，下端拴一小球，把小球拉到A位置，然后放手，仔细观察小球在摆动过程中高度和速度的变化，并说明小球从A→O→B的过程中动能、势能及机械能是怎样变化的．

答案

小球在摆动过程中，摆动的高度逐渐减小，速度也逐渐变慢．从A到O时，重力势能转化为动能；从O到B，动能转化为重力势能，小球最终停下来是由于与空气的摩擦，使机械能转化为了内能．故在这个过程中，机械能的总量是减小的．

完形填空

完形填空
Long ago，some children were playing at seaside when they found a turtle(海龟). They began to beat(打) the turtle. Just at that time, a young man came and said to them, “Stop!” The children ran    1   quickly. The turtle was very thankful and said, “Thanks for your    2  . I truly would like to invite you to a wonderful palace now.”
The young man rode on the back of the turtle and was taken to the secret palace in the sea. When he    3  the palace, he was very surprised and said to the turtle， “What a nice palace!” In order to thank him, the king(国王) of the turtles gave him a very big dinner. He had never seen such a dinner before. He received a warm welcome there and was very    4  everything.
After dinner, the king of the turtles said, “I am going to give you two boxes,    5    you can open only one.” “You mustn’t open both of them. Don’t forget it！” The turtle   6  him. “All right, I will open only one,” the young man promised. At this time, a large wave(浪) sent him out of the sea.
7  he went home, he opened the bigger one of the two boxes. To   8   surprise, the box was full of gold. “My God!” he cried. “I’m   9  now.” Then he thought, “Things in the other box must be expensive, too.” He could not wait any longer. He    10  his promise and opened the other box. As soon as he opened it, he became an old man. His hair turned white. His face looked like an old man over eighty years old. It all happened in a moment. He was sorry for what he did, but it was too late.

A．pleased with

B．careful with

问答题简答题

你知道地球上有几种斑马吗？