题干

在探究动能大小与质量关系的两次实验中,小球从同一高度由静止开始释放时的场景如图所示,木板固定在水平面上,该实验是通过比较木块在木板上滑行的____来比较小球动能大小的,图中错误的操作是____.改正后进行实验,发现木块会从木板右侧滑出,则可以通过____(选填“增大”或“减小”)木块的质量来加以改进.


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答案(点此获取答案解析)

距离,两次实验中未保持木块初始位置相同,增大

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   In many high schools,there are strict rules about using mobile phones. If your phone rings in class,for example,the teacher will be very angry.
   Every mobile phone has a ringtone (铃声). It tells you that someone is calling you. Now,there is a ringtone called “mosquitotone (蚊子铃声)”. Using it,students can receive calls and text messages (短信) in class but the teacher will not realize what is happening. How?
   Mosquitotone has a special sound. Only children and teenagers can hear it. As we get older,we are unable to hear some sounds with high frequencies (频率). As a result,a child or teenager can hear the mosquitotone ringtone, but it's_inaudible_to someone 20 or older.
   But sometimes,people over 20 can hear the ringtone. One British student's phone uses mosquitotone. In class,the student's phone rang. The 32­year­old teacher looked at the student and became unhappy. “I heard that. You know the rule:no mobile phone in class.”
   Not all the students are interested in mosquitotone. Jerry Jones,a high school student of 17,says,“Using mosquitotone too often is bad for our hearing. I may use it for pleasure,but not in class. It's unfair to the teachers!”
   What do parents think of mosquitotone?“I think it is perfect for places like movie theaters,” says Connie Neeson,44.“Think about it. Yon're watching a film and someone's mobile phone rings. Mosquitotone is good because many people don't hear it. However,it also has a bad influence on their study if students use it in class.”