题干

下列说法正确的是(   )

A:“笔尖下发现的行星”是天王星,卡文迪许测出了万有引力常量G的值

B:行星在圆周轨道上保持匀速率运动的性质不是惯性

C:行星绕恒星运动轨道为圆形,则它运动周期的平方与轨道半径的三次方之比 T2R3 =K为常数,此常数的大小与恒星的质量和行星的速度有关

D:匀速圆周运动是速度大小不变的匀变速曲线运动,速度方向始终为切线方向

上一题 下一题 0.0难度 选择题 更新时间:2017-06-03 12:04:14

答案(点此获取答案解析)

B

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    Explore the possibility of using the iPad App Store in the classroom.

    App Name: Bridge Constructor/Cost: $1.99

    Bridge Constructor lets players build increasingly challenging bridges over deep valleys, canals and rivers. Stress tests reveal whether the bridge kids build can withstand continual use from cars, trucks, and more recently, super-heavy tank trucks. Players can choose from among a range of bridge-building materials such as wood, steel, cables and concrete pillars (混凝土柱). Each bridge also has a budget, and there are numerous ways to successfully complete each challenge.

App Name: Pyramid Adventure 3-D/Cost: $13.99

    The interface allows users to fly around the plateau where the pyramids and the Sphinx are located at Giza near Cairo. Interactive, three-dimensional maps let students wander around the labyrinthine tombs and passageways. Uses can examine wall paintings in detail, or view royal statues and objects with a 360-degree feature. To help explain the world of ancient Egyptians, the app offers an accompanying interactive book, specially written by world-famous Egyptologist Zahi Hawass.

    App Name: Grammar Up/Cost: $4.99

    Grammar Up is a multiple-choice quiz system for English grammar. Kids and adults can learn most quickly when playing learning games with real-time error feedback, which Grammar Up provides. The app also offers students practice tests so they can see how much they've learned. A summary is presented at the end of each test, showing the time spent, a score, and the questions answered correctly and incorrectly. The results are also e-mailable.