题目

一体以大小为2m/s的初速度做匀变速直线运动，2s后速度大小变为8m/s，则该物体的加速度大小可能为________。 答案：【答案】3m/s2 5m/s2【解析】已知初速度v0=2m/s，末速度v=8m/s或-8m/s，时间t=2s，设物体的加速度为a，由速度-时间关系式有：分别代入不同的末速度得：a=3m/s2 或 a=-5m/s2 ，加速度的大小取绝对值,则该物体的加速度大小可能为3m/s2 ，5m/s2。阅读下面短文，在空白处填入 1 个适当的单词或括号内单词的正确形式。Looking out of the window of his Ford truck, Bob Fitzgerald sees large, undesirable plants growing in the fields.【1】(visitor) to his neighborhood in Princess Anne, Maryland 【2】(main) see dying forests and empty farmland.Fitzgerald says the land【3】(be) in his family for over 3 centuries. “I’d say in the next 20 years. You’re going to lose【4】very high percentage of that land.”The land around the Chesapeake Bay has been sinking for hundreds of years. But climate change is making things【5】(bad). As sea level rises, salt water is entering rivers and other waterways. As a result, the ground is becoming too salty for crops【6】(grow) on.Maryland’s Eastern Shore is home to some of the oldest farms in North America. Fitzgerald says he has seen big changes during his life.“You just can’t believe【7】it’s been taking things over in the last 15 or 20 years. I can show you land around here that people raised tomatoes on when I was a little boy. And now it’s gone.”Around the world, scientists warn that coastal farms are under【8】(threaten) from rising seas and salt water. A World Bank report estimates rice production in coastal areas of Bangladesh may fall【9】15 percent by the year 2050. Another study found hundreds of millions of people will【10】(force) to move inland because of rising waters.