题干

研究小车匀变速直线运动的实验装置如图(a)所示,其中斜面倾角θ可调,打点计时器的工作频率为50Hz,纸带上计数点的间距如图(b)所示,其中每相邻两点之间还有4个记录点未画出.

①部分实验步骤如下:

A.测量完毕,关闭电源,取出纸带

B.接通电源,待打点计时器工作稳定后放开小车

C.将小车依靠在打点计时器附近,小车尾部与纸带相连

D.把打点计时器固定在平板上,让纸穿过限位孔

上述实验步骤的正确顺序是:____(用字母填写)

②图(b)中标出的相邻两计数点的时间间隔T=____s

③计数点5对应的瞬时速度大小计算式为v5=____

④为了充分利用记录数据,减小误差,小车加速度大小的计算式应为a=____

上一题 下一题 0.0难度 选择题 更新时间:2017-10-14 12:01:13

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DCBA,0.1,s4+s52T,

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    A 17-year-old boy, caught sending text messages in class, was recently sent to the vice principal's office at Millwood High School in Halifax, Nova Scotia. The vice principal, Steve Gallagher, told the boy he needed to focus on the teacher, not his cellphone. The boy listened politely and nodded, and that's when Mr. Gallagher noticed the student's fingers moving on his lap. He was texting while being scolded for texting. “It was a subconscious act,” says Mr. Gallagher, who took the phone away. “Young people today are connected socially from the moment they open their eyes in the morning until they close their eyes at night. It's compulsive.”

    A study this year by psychology students at Covenant College in Lookout Mountain, Ga., found that the more time young people spend on Facebook, the more likely they are to have lower grades and weaker study habits. Heavy Facebook users show signs of being more sociable, but they are also more likely to be anxious, hostile or depressed. (Doctors, meanwhile, are now blaming addictions to 'night texting' for disturbing the sleep patterns of teens.)

    Almost a quarter of today's teens check Facebook more than 10 times a day, according to a 2009 survey by Common Sense Media, a nonprofit group that monitors media's impact on families. Will these young people get rid of this habit once they enter the work force, or will employers come to see texting and 'social-network checking' as accepted parts of the workday?

    Think back. When today's older workers were in their 20s, they might have taken a break on the job to call friends and make after-work plans. In those earlier eras, companies discouraged non-business-related calls, and someone who made personal calls all day risked being fired. It was impossible to imagine the constant back-and-forth texting that defines interactions among young people today.

    Educators are also being asked by parents, students and educational strategists to reconsider their rules. “In past generations, students got in trouble for passing notes in class. Now students are skilled at texting with their phones still in their pockets,” says 40-year-old Mr. Gallagher, the vice principal, “and they're able to communicate with someone one floor down and three rows over. Students are just fundamentally different today. They will take suspensions rather than give up their phones.”