问题 选择题

关于参考系,下列说法正确的是    (    )

A.运动的物体不能作为参考系

B.选定某物体为参考系是为了描述其他物体的运动

C.选择不同的物体做为参考系来观察同一物体的运动,得到的结论应是一样的

D.研究地面上物体的运动,必须选地球为参考系

答案

答案:B

题目分析:一切物体都在运动,要研究物体的运动必须选取参考系.参考系是指研究物体运动时所选定的参照物体或彼此不作相对运动的物体系;参考系的选取是任意的,如何选择参照系,必须从具体情况来考虑,一般情况下我们以地面或地面上的物体作为参考系.

A. 参考系的选取是任意的,所以运动的物体也可以作为参考系,比如以运动的汽车为参考系,研究车内人的运动情况,A错误

B. 一切物体都在运动,要研究物体的运动必须选取参考系.B错误

C. 选取不同的物体作为参考系,得出的结论可能不同,比如当以路旁的树木为参考系研究行驶的车中的乘客的运动情况,和以车中的司机为参考系研究车中的乘客的运动情况,两种结论是不同,C错误

D. 参考系的选择是任意的,可以是相对地面不动的物体,也可以是相对地面运动的物体,如何选择参照系,必须从具体情况来考虑,一般情况下我们以地面或地面上的物体作为参考系,D错误,

点评:只有掌握了参考系的概念我们才能顺利解决此类题目,所以我们要加强基本概念的理解和掌握.

选择题
单项选择题

Every generation has its emblematic boy’s toy. once upon a time there was the golf cart: a little toy car specifically designed for middle-aged men too rich to care about looking ridiculous. Later came the beach buggy, a briefly fashionable, wildly impractical, single-terrain vehicle. one might include the motorcycle or the snowmobile on this list, were they not, in certain contexts, quite useful, but there is no doubt which pointless recreational vehicle has captured the imagination of the landed, middle-aged celebrity: it’s the quad bike.

What is it about this squat, ungainly, easy-to-flip machine that celebrities love so much As recreational vehicles go, the quad bike is hardly sophisticated. They are to the countryside what the jet-ski is to Lake Windermere. "There’s nothing cool about a quad," says Simon Tiffin, editor of a well-known magazine. "It’s a strange thing to want to hare round beautiful bits of the country in a petrol-guzzling machine."

But celebrities love quad bikes. Musicians, comedians, DJs, actors and sportsmen have all been photographed aboard quads. "They’re the latest rich person’s toy," says Tiffin. "Spoilt children get them for Christmas." Provided you’ve got a large estate to go with it, however, the quad bike can remain a secret indulgence. You can go out and tear up your own piece of countryside without anyone knowing you’re doing it.

The quad bike’s nonsensical name -- "quad" means four, but "bike" is an abbreviation of "bicycle," which means two -- that comes to six -- hints at its odd history. Originally the ATV, or all-terrain vehicle, as quads are sometimes known, was developed in Japan as a three-wheeled farm vehicle, an inexpensive mini-tractor that could go just about anywhere. In the 1980s the more stable four-wheeled quad was officially introduced -- enthusiasts had been converting their trikes for some time -- again primarily for farming, but its recreational appeal soon became apparent. At the same time a market for racing models was developing.

Paul Anderson, a former British quad racing champion, says the quad’s recreational appeal lies in its potential to deliver a safe thrill. "It’s a mix between a motorbike and driving a car; when you turn a corner, you’ve got to lean into the corner, and then if the ground’s greasy, the rear end slides out," he says. "Plus they’re much easier to ride than a two-wheeled motorcycle." The quad bike, in short, provides middle-aged excitement for men who think a Harley might be a bit dangerous. Anderson is keen to point out that quad bikes are, in his experience, much safer than motorcycles. "With quad racing it’s very rare that we see anybody having an accident and getting injured," he says. "In the right hands, personally, I think a quad bike is a very safe recreational vehicle," he adds.

Outside of racing, quad bikes are growing in popularity and injuries have trebled in the last five years. Although retailers offer would-be purchasers basic safety instructions and recommend that riders wear gloves, helmets, goggles, boots and elbow pads, there is no licence required to drive a quad bike and few ways to encourage people to ride them wisely. Employers are required to provide training to workers who use quad bikes, but there is nothing to stop other buyers hurting themselves.

For the rest of the world, quad bikes are here to stay. They feature heavily in the programmes of holiday activity centres, they have all but replaced the tractor as the all-purpose, agricultural workhorse and now police constables ride them while patrolling the Merseyside coastline.

It has more or less usurped the beach buggy, the dirt bike and the snowmobile, anywhere they can go the quad bike can. They even race them on ice. You can’t drive round Lake Windermere on one, or at least nobody’s tried it yet. Just wait.

Which of the following statements is NOT true about quad bikes?()

A.They can be ridden even on ice.

B.They can be used a great deal on farms.

C.They are driven by the police.

D.They are replaced by horses.