题目

Did you know that, in 2016, over 18 million people attended classical concerts in Germany? That’s more people than those who went to main league football matches! Earlier this year, Germany continued its celebration of classical music with the opening of a new concert hall in the heart of Hamburg. Germans are incredibly proud of it and it’s the first thing I show to my friends when they come to visit. Known as the ‘Elphi’ by the locals, the Elbphilharmonie is a beautiful tower of glittering glass sitting atop an old warehouse by the banks of the river Elbe. The plaza (露天广一质点做变速直线运动，若前t/4 内的平均速度为6m/s，后3t/4时间的平均速度为10m/s，则这段时间t内的平均速度为__________________;若质点前一半位移的平均速度为3m/s，后一半位移的平均速度为6m/s，则这段位移的平均速度为____________________.