题干

如图所示,两光滑斜面在B处连接,小球从A处由静止释放,经过B、C两点时速度大小分别是3m/s和4m/s,AB=BC.设球经过B点前后速度大小不变,则下列判断正确的是(   )

A:球在AB,BC段的加速度大小之比为4:3

B:球由A运动到C的过程中平均速率为2.1m/s

C:小球在AB,BC段的运动时间之比为7:4

D:小球从B运动到C过程中平均速度大小为3.5m/s

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答案(点此获取答案解析)

B,D

同类题5

阅读下面短文, 从方框内选择恰当的句子填入文中空白处,使短文内容完整、 意思连贯。

  In 2011, when British photographer David J. slater was visiting a park in Indonesia, his camera was taken away by a group of black monkeys. The result was hundreds of monkey selfies(自拍照)。The best ones show a monkey smiling toothily for the camera____

Nobody knew they would create a copyright(版权) battle three years later.

  Last month, a website put the monkey selfies online under a collection of free photos without Slater's permission(允许). ____ .

  However, the website refused to do so. They said that according to US copyright law, whoever pushes the button on the camera owns the copyright to the photo. ____.

  They Said,“US copyright law says that works that come from a non-human source can't ask for copyright. That means monkeys don't own copyright”.

____ He said he bought the cameras; he spent a lot of money traveling to Indonesia and it was his carelessness that allowed the monkeys to take his cameras away.All these have made him own the pictures, no matter who pushed the button .In a sense,the monkeys helped him take the photos, Slater said.

   ____Who do you think will win this battle?

A· It was the monkeys but not Slater that pushed the button.

B.As of now, there has been no result in the Monkey Selfie case.

C. Slater then sold the photos and they became popular on the Internet

D. Slater asked the website to take them down since he owns the copyright

E. Slater argues that the pictures belong to him as they were taken from his camera.