用打点计时器测速度实验中，打点计时器打出一纸条，共选出A、B、C、D四个计数点，相邻两计数点间还有四个点未画出，用交流电频率为50赫兹，纸带上各点对应尺上的刻度如图，AD段的平均速度______m/s，B点的瞬时速度______m/s．
根据平均速度定义得
=. v
=16m/sx t
根据匀变速直线运动中中间时刻的瞬时速度等于该过程中的平均速度得：
vB=
=15m/sxAC tAC
故答案为：16，15．
Wen Jiabao arrived in Singapore yesterday for an official visit to the country. It is the first visit by a Chinese premier to Singapore in eight years. In the arrival statement, When said he is looking forward to the meeting with Singing pore on ways to deepen East Asian cooperation between two nations so as to contribute to the building of a peaceful, harmonious relationship. Premier Wen Jiabao and Singapore Prime Minister Lee Hsien Loong agreed to jointly develop an environmentally friendly city in northeastern China. The city will be a model for sustainable development, a Singapore government statement said.The”Sino-Singapore Tjanjin Eco—city” will be developed by a joint venture formed by Chinese and Singapore companies.”This eco-city, to be built in Tianjin, well become another highlight in our relations,” When said after signing an agreement with Lee, who agreed,“On the Singapore side, on all levels,we’ll give this project our full support.” The two sides will share expertise and experiences in urban planning, environmental protection, resources conservation,recyeling,use of renewable resources and wastewater re-use. China’s economil planning agency issued a set of guidelines earlier this month welcoming foreign investment in environmentally friendly areas such as recycling,”clean”industries and environmental protection. Bilateral relations between China and Singapore have seen big progress even though the two countries established diplomatic ties only 17 years ago, When said during his talks with Lee. China and Singapore have also kept close contact and coordination on regional issues, he added. When said China and Singapore are both important Asian countries that share common interests in many areas. Title: Wen’s visit to Singapore
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