问题 问答题

调节水龙头,让水一滴滴流出,在下方放一盘子,调节盘子高度,使一滴水滴碰到盘子时,恰有另一滴水滴开始下落,而空中还有一滴正在下落中的水滴,测出水龙头到盘子的距离为h,从第一滴开始下落时计时,到第n滴水滴落在盘子中,共用去时间t,则此时第(n+1)滴水滴与盘子的距离为______;  当地的重力加速度为______.

答案

由题意可知,水滴将h分成时间相等的2份,2份相等时间的位移比为1:3,总高度为h,所以第n滴水滴落在盘子中,第(n+1)滴水滴与盘子的距离为

3h
4

从第一滴水离开水龙头开始,到第n滴水落至盘中(即N+2滴水离开水龙头),共用时间为t(s),知道两滴水间的时间间隔为△t=

t
n+1
所以水从水龙头到盘子的时间为t′=
t
n+1
,根据h=
1
2
gt′2,得:g=
(n+1)2
2t2
h

故答案为:

3h
4
(n+1)2
2t2
h

单项选择题 A1/A2型题
单项选择题

Recently, I flew to Las Vegas to attend a meeting. As we were about to arrive, the pilot announced with apology that there would be a slight (16) before setting down. High desert winds had (17) the airport to close all but one runway. He said that we would be (18) the city for a few minutes waiting to (19) . We were also told to remain in our seats meanwhile with our seat belts fastened (20) there might be a few bumps(颠簸). Well, that few minutes turned into about four-five minutes, including a ride that would make a roller coaster(过山车) (21) by comparison. The movement was so fierce that several passengers felt (22) and had to use airsickness bags. As you might guess, that’ s not a good thing to have happen in a(n) (23) space because it only (24) to increase the discomfort of the situation.

About twenty minutes into the adventure, the entire airplane became very (25) There was now a sense of anxiety and fear that could be (26) noticed. Every passenger simply held on for dear life …except one. A (27) was having a good time! With each bump of the (28) , he would let out a giggle (咯咯地笑)of delight. As I observed this, I (29) that he didn’t know he was supposed to be afraid and worried about his (30) . He neither thought about the past nor about the future. Those are what we gown--ups have learned from (31) . He was (32) the ride because he had not yet been taught to fear it. Having understood this, I took a deep breath and (33) back into my seat, pretending I was (34) on a roller coaster. I smiled for the rest of the flight. I even (35) to giggle once or twice, much to the chagrin(随恼) of the man sitting next to me holding the airsickness bag.

35()

A.teachers 

B.books 

C.experience 

D.practice