There are lots of that students have to follow in school.
A:exercises
B:problems
C:skills
D:rules
矿井里的升降机,由静止开始匀加速上升,经5s速度达到6m/s后,又以此速度匀速度上升10s,然后匀减速上升,又经10s停在井口.求矿井的深度.
下列有关内、外力作用叙述正确的是( )