一矿井深为125m，在井口每隔一相同时间自由下落一个小球．当第6_爱下问搜题

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问题问答题

一矿井深为125m，在井口每隔一相同时间自由下落一个小球．当第6个小球刚从井口开始下落时，第1个小球恰好到达井底，求：

（1）相邻两个小球开始下落的时间间隔；

（2）这时第4个小球距井底的距离．（g=10m/s²）

答案

解；（1）设相邻两球的时间间隔为t₀，那么第一个小球的运动时间为5t₀，

由h=

1

2

g(5t0)2得

t0=

2h

25g

=

2×125

250

s=1s

（2）第4个下落的时间为t=2t₀=2s

下落的高度为h₁=

1

2

gt2=20m

距井底的距离为h₂=H-h₁=125-20=105m

答：

（1）相邻两个小球开始下落的时间间隔为1s；

（2）这时第4个小球距井底的距离为105m．

填空题

用所给单词的适当形式填空。

1. If I (have) one million dollars, I would give it to the hospital.

2. About millions of sheep (keep) in that country.

3. My brother always asks me (take) him to the net bar in the city.

4. If I _ (be) you. I would give him some food, not money.

5. You'd better (take) a long walk with your friends if you are still nervous.

6. Don't stay up too late before (go) to bed.

7. I want to know if everyone else (bring) a present to our teacher.

8. If your father were there last night, he ______ (help) us finish the work.

9. Everyone laughs at my old sweater, so I stop_____ (wear) it.

10. If you are still nervous, ___ _ (take)a long walk can be helpful to you.

多项选择题

哪些营养因素也是压疮发生的独立危险因素（）

A.体重减轻

B.蛋白质或能量摄入不足

C.脱水

D.低血清蛋白

E.高龄