搜题请搜索小程序“爱下问搜题”
问题 计算题

（10分）一个屋檐距地面9 m高，每隔相等的时间就有一个水滴从屋檐自由落下。当第4滴水刚要离开屋檐时，第1滴水正好落到地面，求此时第2滴水离地的高度。（g =" 10" m/s2）

答案

5m

题目分析：根据匀变速直线运动公式可知初速度为零的水滴在连续相等的时间内的位移之比为1：3：5

故可解得第2滴水离地的高度为：。

判断题

10÷0.5=20所以10是0.5的倍数，0.5是10的因数。[ ]
查看答案
单项选择题

Another critical factor that plays a part in susceptibility to colds is age. A study done by the University of Michigan School of Public Health revealed particulars that seem to hold true for the general population. Infants are the most cold-ridden group, averaging more than six colds in their first year. Boys have more colds than girls up to age three. After the age of three, girls are more susceptible than boys, and teenage girls average three colds a year to boys’ two.
The general incidence of colds continues to decline into maturity. Elderly people who are in good health have as few as one or two colds annually. One exception is found among people in their twenties, especially women, who show a rise in cold infections, because people in this age group are most likely to have young children. Adults who delay having children until their thirties and forties experience the same sudden increase in cold infections.
The study also found that economics plays an important role. As income increases, the frequency at which colds are reported in the family decreases. Families with the lowest income suffer about a third more colds than families at the upper end. Lower income generally forces people to live in more cramped quarters than those typically occupied by wealthier people, and crowding increases the opportunities for the cold virus to travel from person to person. Low income may also adversely influence diet. The degree to which poor nutrition affects susceptibility to colds is not yet clearly established, but an inadequate diet is suspected of lowering resistance generally.

The phrase "people in this age group" underlined in Paragraph 2 refers to ______ .

A．infants



B．people in their twenties
C．people in their thirties and forties
D．elderly people
查看答案