在光滑的地面上，质量为m1的物体以速度v0与原来静止的质量为m2的物体发生弹性正
题型：计算题
问题：
在光滑的地面上，质量为m1的物体以速度v0与原来静止的质量为m2的物体发生弹性正碰，碰撞后它们的速度分别为v1和v2，
（1）推导出用m1、m2、v0表示的v1和v2的表达式；
（2）若要m1球发生反弹，推导出m1、m2的大小关系式。
题型：计算题
Tre’S mom，Christina Thompson, cannot believe how much her son already learned this year in his full-day, free pre-school class in Oklahoma City. “Since he’s been in school his vocabulary has increased surprisingly,” Thompson says. “The other day he came home and said, ‘You know what ，mom? You are being ridiculous，” Thompson laughs quietly. “And then he asked, ‘Do you know what ‘ridiculous’ means, mom?’” Tre knows the entire alphabet, his numbers to 100，and he’s starting to read. And letters and numbers aside, Thompson is most struck by how fast Tre is absorbing vocabulary and language.
Of course, not all pre-school is created equal. High quality pre-schools have well-trained, well-educated teachers in the classroom (much like Tre Thompson’s teacher Mrs. Wallace, who uses play-based learning to teach both academics and social skills and can rattle off (飞快说出） a battery of data on how well her students are progressing towards their year-end goals). Texas can also offer a model for educator development: its Texas School Ready! Campaign has proven to increase the quality of participating pre-schools by providing early childhood teachers with coaching, professional development, research-based curriculum (课程)，and progress monitoring. States and districts should also combine pre-school with the K-12 system, as Oklahoma does ，so that children enter kindergarten smoothly.
Oklahoma is one of the leading states in providing students like Tre with free ，full-day pre-school. And the results are already paying off: According to a 2012 study, Oklahoma kids that went through pre-school showed vocabulary gains 28% higher than those of children without pre-school, and math gains 44% higher than non-pre-school kids. And we know that high-quality pre-school doesn’t just mean higher scores in elementary school. They were more likely to have graduated from high school and less likely to have committed a violent crime. They also earned more money and were more likely to be employed.
We know pre-school works, so let’s stop talking and start building a system where all children have access to excellent early childhood education. As any well-educated four year old could tell us, not doing so would be ridiculous.
小题1:The case of Tre in the first paragraph serves as the evidence of______.
A．children’s disrespect towards parents
B．the bad performance of students at school
C．the positive effect of pre-school on children
D．Thompson’s doubt about her son’s education小题2:At high quality pre-schools, children may learn by______
A．playing
B．modelling
C．researching
D．monitoring小题3:It can be inferred that______.
A．children can not enter kindergarten without pre-school
B．Oklahoma is the best state offering full-day pre-school
C．all pre-schools have well-trained, well-educated teachers
D．kids with pre-school may be better equipped for their future小题4:What would be the best title for the passage?
A．Not all pre-school works
B．All pre-school is created equal
C．We owe our kids universal pre-school
D．Pre-school goes well with K-12 system