搜题请搜索小程序“爱下问搜题”
问题 计算题

在一次爆破中，引火线的长度为96cm，燃烧速度是0.8cm/s，点火者点燃引火线以后以5m/s的速度跑，能否在爆炸前跑到500m以外的安全地方？

答案

解：方法一：导火线燃烧完所用时间：t1===120s，

人跑到安全地区需用的时间：t2===100s，

因为 t2＜t1，所以能跑到．

方法二：t1===120s，

人在t1内能通过的路程s2=v2t1=5m/s×120s=600m＞500m，

所以能跑到．

方法三：人跑到安全地区所需时间：t2===100s，

经100s导火线燃烧的长度：L=0.8cm/s×100s=80cm＜96cm，

在导火线烧完前人能到安全地区．

选择题

在梯形ABCD中，AD∥BC，AD：BC =1：3，其对角线的交点为O，则S△AOD：S△COD：S△BOC等于 [ ]

A.1：2：3

B.1：2：7

C.1：3：9

D.1：4：9
查看答案
单项选择题

"I would almost rather see you dead. " Bobert S. Cassatt, a leading banker of Philadelphia, shouted when his twenty-year-old eldest daughter announced that she wanted to become an artist. In the 19th century, playing at drawing or painting on dishes was all right for a young lady, but serious work in art was not. And when the young lady’ s family racked among the best of Philadelphia’s social families, such an idea could not even be considered.

That was how Mary Cassatt, born 1844, began her struggle as an artist. She did not tremble before her father’s anger, she opposed him with courage and at last made him change his mind. Mary Cassatt gave up her social position and all thoughts of a thousand and a family, which in those times was unthinkable for a young lady. In the end, after long years of hard work and perseverance, she became America’s most important woman artist and the internationally recognized leading woman painter of the time.

What made Mary Cassatt’ s "struggle" to become a recognized artist especially hard（）

A．She was a woman.

B．Her father opposed her.

C．She had no social position.

D．She didn’t come from an artist’s family.
查看答案