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如图所示,一个水平放置的圆桶正以中心轴匀速运动,桶上有一小孔,桶壁很薄,当小孔运动到桶的上方时,在孔的正上方h处有一个小球由静止开始下落,已知圆孔的半径略大于小球的半径,为了让小球下落时不受任何阻碍,h与桶的半径R之间应满足什么关系(不考虑空气阻力)?

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解:设小球下落h所用时间为 ,经过圆桶所用时间为 ,则:

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    Robot are about to enter our lives. From doing housework, entertaining and educating our children, to looking after the elderly, scientists say we will soon be welcoming robots into our homes and workplaces.

    Researchers believe we are on the cusp (过渡点) of a robot revolution that will mirror the quick growth of the computer revolution. They are developing new laws for robot behavior, and designing new ways for humans and robots to communicate.

    “I think robots will change who we are, just as eyeglasses and fire changed who we were before, says Rodney Brooks, a director of the MIT Computer Science and Artificial Intelligence Laboratory.

    Some ideas and technologies may sound like science fiction, but they are fast becoming science fact. Robots scientists invented are already beginning to perform everyday tasks like cleaning our floors. The latest types from Japan are able to help the elderly to get out of bed or get up after a fall. They can also remind them when to take medication (药物), or even help wash their hair.

    “Robot now are not human-like. For example they are things like automatic (自动的) beds and wheelchairs,” says Prof Hiroshi Ishiguro at Osaka University, Japan. He believes the time is coming when robots start looking less like machines, and more like us. “In the near future we are going to use more human-like robots. I really think so, says Prof Ishiguro.

    Prof Maja Mataric at the University of Southern California agrees. “I'm very excited about the fact that today we are trying to make robots that look like human beings,” she says.

    “I believe we love robots because they're reflections (反映) of ourselves,” says Ken Goldberg, director of the Berkeley Center for New Media at the University of California at Berkeley.

    “Robots could be used in education, learning, and healthcare, where social support is important,” says Dr. Cynthia Breazeal, director of the Personal Robots Group at MIT.