三道物理题.关于加速度自由落体那些的,A falling stone takes 0.28s to travel past a w_英语解答

三道物理题.关于加速度自由落体那些的,
A falling stone takes 0.28s to travel past a window 2.2m tall.From what height above the top of the window did the stone fall?
A rock is dropped from a sea cliff(悬崖）,and the sound of it striking （撞击）the ocean is heard 3.2s later.If the speed of sound is 340m/s,how high is the cliff?
A stone is dropped from the roof(顶） of a high building.A second stone is dropped 1.5s later.How far apart are the stones when the second one has reached a speed of 12.0m/s?

人气：138 ℃　时间：2019-08-20 10:16:06

解答

1)
距离差求得到窗顶的时间t：1/2g(t+0.28)²-1/2gt²=2.2
从而离窗顶高度为：h=1/2gt²
解得：t=0.662s,h=2.15m
2)总时间为下落时间与声音回时间之和
下落：1/2g×t1²=h
返回：340×t2=h
总时间：3.2=t1+t2
解得：t1=3.06s,t2=0.135s,h=46.0m
3)
第二块达到速度时：g×t2=12
第一块此时的下落时间：t1=t2+1.5
两者位移差：s=1/2g×t1²-1/2g×t2²
解得：t2=1.22s,t1=2.72s,s=29.0m