如图所示，两个质量不同的物体A和B，分别从两个相同高度光滑斜面和光滑圆弧斜坡的顶点，从静止开始下滑到底部，下列说法正确的是
A．它们到达底部时的速度大小相等
B．下滑过程中重力做的功相等
C．它们在顶点时的机械能相等
D．它们到达底部时的动能相等
答案：A
题目分析：两轨道光滑，故机械能守恒，所以有
，故可知两物体到达底部时速度大小相等，所以A正确；因质量m不同，所以重力做功不同、到达底部时动能不同、开始时的机械能不同，所以B、C、D错误。
| 用方框内所给单词的适当形式填空。 | |
the closest people to you in the world. But a lot of middle school students have a problem. They feel they're not as 3 _______ to their parents as before. They even think their parents are unfair to them. Some students complain that their parents say a lot to them, but never 4_______ to them. Some of them even say it 5_______ . "My parents don't allow me to play computer games, 6_______ other classmates are doing that". Others say, when they're 7_______ phone calls to friends, their parents like to ask if they're speaking to a boy or a girl. These make them very 8_______. Some students even decide to leave home. But they don't know running away may bring them some more problems. Show your parents you're growing up. Then they'll feel you're no 9_______ a small child. 10_______ you follow the advice, you'll have a happy life and never think of running away. |