质量 M = 6.0×10 3 kg 的客机,从静止开始沿平直的跑道匀加速滑行,当滑行距离 l = 7.2×10 2 m 时,达到起飞速度 v = 60 m/s. 求: (1) 起飞时飞机的动能多大? (2) 若不计滑行过程中所受的阻力,则飞机受到的牵引力为多大? (3) 若滑行过程中受到的平均阻力大小为 F = 3.0×10 3 N ,牵引力与第 (2) 问中求得的值相等,则要达到上述起飞速度,飞机的滑行距离大?
【简答题】According to a new study, preschool boys perform better on tests that measure learning and other important skills when they are in classes that have more girls than boys. This doesn’t seem to apply to...