(1)求;
(2)设炸药爆炸时释放的化学能为且完全转化为两小球动能,求从爆炸到发生第
一次碰撞的时间t。
(1)(2)
Little __________ about him and he seems to like playing alone. [ ]
A. we know
B. we don't know
C. don't we know
D. do we know
为什么回风巷道内严禁使用架线电机车?