题干

如图所示,小球在A点由静止开始释放,向右侧摆动。B点是小球摆动的最低点,C点是小球摆到右侧最高点,且A、C两点到B点的竖直距离hA>hC。在小球从B点摆动到C点的过程中(    )

A:小球的机械能总量逐渐变小

B:小球运动状态保持不变

C:小球的动能全部转化为重力势能

D:绳的拉力对小球做了功

上一题 下一题 0.0难度 选择题 更新时间:2012-04-23 10:57:45

答案(点此获取答案解析)

A

同类题4

阅读下面的短文,掌握其大意,然后从短文后各题所给的A、B、C、D四个选项中,选择最佳选项。

    Maddy Cullen became a heroine last month. Thanks to her quick thinking, she and Dave Lewis were saved from danger in the 1 .

    Maddy and Dave went to the Scottish Highlands with a group from the Music Now Festival. In the afternoon, the group went 2 on the lake, but Maddy and Dave went hang-glider(滑翔) instead. Unfortunately, above the famous lake Loch Ness, the hang-glider flew into a sudden storm and knocked on a mountain out of 3 . Both Maddy and Dave jumped off the hang-glider before it crashed down(坠毁). They dropped safely in the mountains. But Dave couldn't walk because his right leg was badly injured. He and Maddy had to stay in the mountains and waited for rescuers. They had no food or water, so they were hungry, thirsty and 4 . They felt very worried before the sun set. Then Maddy had a very good idea. She collected many stones and formed a large sign “SOS” on the ground so that pilots in the helicopter could find them 5 .

    Meanwhile, group leader Rob Townsend was also worried when he found Maddy and Dave didn't sail with them. There were no public 6 anywhere nearby. He had to walk a long way to call the police to look for the missing teenagers. A few minutes later, a police helicopter flew over Loch Ness, and the pilot saw Maddy's message from above easily. Dave and Maddy were 7 up and flown to hospital in Inverness quickly.

    A week ago, Maddy spoke to a reporter from the newspaper. “We were very 8 when the helicopter arrived,” she said. “The police told Dave not to move and they carried him into the helicopter. They asked us to put on dry clothes and 9 some hot soup to us. They were great.”

    “It was all because of me,” Dave said. “Rob told us to wear walking boots, and he told us not to leave the group. But I did not listen. I was very silly.”

    The police 10 . On its radio news, they asked walkers in the Highlands to follow instructions carefully and not to take any adventures.