题干

如图AOB是光滑轨道,A点的高度H大于B点的高度,让小球从A点由静止开始自由滑下,沿轨道AOB到达B点后离开(不计空气阻力。则小球离开B点后的运动轨迹最符合实际的是哪条?为什么?

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c正确,小球从A点由静止滑下,所以小球的机械能等于A点时的重力势能,整个过程中机械能守恒。因为在最高点时小球仍运动,故其最高点应略低于起点A,这与c图线相符。

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    With more and more cars on the road, traffic jams (堵车) are inevitable. Traffic jams can lead to more accidents as there are more cars, with more people trying to get to their destination, all the while getting worse. Although it's impossible to avoid traffic jams altogether, there are some tips you can follow to reduce the amount of time on the road.

    Check for traffic jams before you leave. You can listen to the radio for traffic news, or check on the Internet to get up-to-minute information on traffic. If the route you want to take is heavy with traffic, you can choose another.

    Look for a different route all the time. Most traffic jams happen on busy roads. Using country roads could avoid a lot of traffic. Although the distance you may have to travel is further, it can work out quicker.

    Set your car radio to receive traffic bulletins. Many new car stereo systems (汽车音响系统) are equipped with a radio system by which you can hear the traffic channel. This way you can get the latest traffic information and change your journey if necessary.

    __________. Most traffic jams usually occur(发生) during rush hour, so try to avoid this time period if possible. Some jobs offer flexible working hours so that you can travel to work outside of rush hour. Some jobs even allow you to work at home so as to avoid moving altogether. Ask your manager to see what you can do if traffic is a problem for you.

    Use public transport instead. The easiest way to avoid traffic jams is to take buses or the underground instead of driving your own car. Not only will you avoid traffic jams but you will most likely be saving money.