如图所示,固定在水平面上的斜面倾角为θ,长方体木块A质量为M,其PQ面上钉着一枚小钉子,质量为m的小球B通过一细线与小钉子相连接,小球B与PQ面接触,且细线与PQ面平行,木块与斜面间的动摩擦因数为μ。若木块匀加速下滑,则小球对木块的压力大小为____________.
The Communist Party of China (中国共产党) has (it) 100﹣year anniversary this year.
The (seven) Big Data Expo was held successfully in Guiyang in May,2021.
Mary doesn't (real) care if her friends are the same or different.
If I'm available tomorrow afternoon,I (visit)the city museum with my brother.
We couldn't do all the work by ( us).