一个小球从距离地面20m的高空下落，做自由落体运动（g取10m/s2）_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题问答题

一个小球从距离地面20m的高空下落，做自由落体运动（g取10m/s²）．求：

（1）小球落地时的速度大小；

（2）小球落地前最后1s时间内下落的高度．

答案

（1）由v²=2gh

代入数据得：v=

2×10×20

=20m/s

（2）由h=

1

2

gt²可知，小球下落2s后落地，则小球第1s内下落的高度为：

h₁=

1

2

gt²=

1

2

×10×1=5m

所以小球落地前最后1s内下落的高度

h₂=h-h₁=20-5=15m

答：（1）小球落地时的速度大小为20m/s；

（2）小球落地前最后1s时间内下落的高度为15m．

单项选择题

热电阻型温度传感器将与温度变化成比例的阻值信号转换成（）的电信号。

A.0～5VDC

B.0～10VDC

C.0～15VDC

D.0～20VDC

填空题

用括号中所给单词的适当形式完成下列句子。每空格限填一词。

1. Mr. White lives on the_______ floor in that building. (five)

2. Walking in the space is one of the _______ of our time. (wonder)

3. Tom will study still _______ next term. (hard)

4. He is very careless, so he is _______ to be in charge of the experiment. (fit)

5. The plane landed _______ at last after flying in the storm for about one hour. (safe)

6. Have you ever seen how to _______ a cow? (milk)

7. Not everyone enjoys fast food. Jack is the one who _______ hamburgers. (like)

8. At the end of every year, some people go back to their _______ homes.(national)