题干

总质量为M的小车ab,原来静止在光滑的水平面上.小车的左端a固定一根不计质量的弹簧,弹簧的另一端放置一块质量为m的物体C.已知小车的水平底板光滑,且M>m,开始时,弹簧处于压缩状态,如图,当弹簧突然释放后,物体c离开弹簧向b端冲去,并跟b端粘合在一起,那么,以下说法中正确的是(   )

A:物体c离开弹簧时,小车一定向左运动

B:物体c离开弹簧时,小车运动的速率跟物体c相对小车运动的速率之比为 mM

C:物体c离开弹簧时,小车的动能与物体c的动能之比为 mM

D:物体c与车的b端粘合在一起后,小车立即停止运动

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答案(点此获取答案解析)

A,B,C,D

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    Michelin inspectors, the super secret spies of the restaurant industry, are the anonymous (匿名的) keepers of the famous Michelin star rating. They've been writing anonymous reports of restaurants for over 100 years.

    “We say it's a little like the CIA,” said inspector “M” with a laugh. She asked that her identity not be revealed. “My whole life is staying under the radar, staying away from cameras, using fake names, trying to steal in and out of restaurants quietly.”

    Along with their boss, Jean Luc Naret, the director of the Michelin Guide, about 90 inspectors around the world decide which restaurants will win the cooking equivalent (等价物) of an Oscar, the Nobel Prize and Megamillions jackpot (百万彩票) all at once. The Michelin Guide covers 23 countries, and out of the 45,000 rated restaurants, less than 100 have the top rating — only nine American restaurants carry three stars.

    If the name “Michelin” brings the tires on your car to mind, you're not too far off. The Michelin rating began in France in 1900 as a marketing trick. The Michelin brothers thought their customers would bum more rubber if given a list of hotels and restaurants to explore.

    Inspector “M” admitted being an inspector leads to a lonely dining life. “Most of the time we dine alone,” she said. “It gives us the ability to really focus on the food and the atmosphere and capture the entire experience.” To cover their tracks, “M” said sometimes two inspectors will dine together and write two separate papers. It's better than saying “table for one”, right?

    “When you're really, really into food and very crazy about food, everything else that's going on around you isn't so important,” she said.