题目

一物体受到三个共点力的作用，下面能使物体处于平衡状态的是A.F1=7 N，F2=8 N，F3=9 NB.F1=8 N，F2=2 N，F3=1 NC.F1=7 N，F2=1 N，F3=5 ND.F1=10 N，F2=10 N，F3=1 N 答案：解析：三力中某两个力的合力|F1-F2|≤F12合≤F1+F2.若另一个力F3的大小在F12合的取值范围内，则这三个力的合力可能为零，物体可能平衡.答案：AD 用下列词组或单词的正确形式完成句子。 come about  build up   even if  result in   subscribe toquantities of  state  keep on  compare to  opposed to1. We__________gaining money by cutting the trees along the river bank.2. The students all__________  the idea that they would take a trip to the hill in the spring.3. I have some difficulties , but they are nothing______ yours.4. As soon as the accident_________,we called 110.5. The headmaster_________that those who break the rules must be punished.6. I will go there_________I have to crawl on my knees.7. The police found _________ drugs under his bed and above his ceiling.8. Though it was snowing, they_________cleaning the streets.9. They tried to _________friendship with the developing countries.10. The heavy fog can easily _________ many traffic accidents in winter.