题目

做匀速圆周运动的两物体甲和乙，它们的向心加速度分别为a1和a2，且a1>a2，下列判断正确的是( )A.甲的线速度大于乙的线速度B.甲的角速度比乙的角速度小C.甲的轨道半径比乙的轨道半径小D.甲的速度方向比乙的速度方向变化快 答案：【答案】D【解析】由于不知甲和乙做匀速圆周运动的半径大小关系，故不能确定它们的线速度、角速度的大小关系，故ABC错误．向心加速度是表示线速度方向变化快慢的物理量，a1>a2，表明甲的速度方向比乙的速度方向变化快，选项D正确；故选D.2、阅读短文，根据所读内容在文后1—10 的空格里填上适当的单词或短语。注意每空不超过3个单词。 Why must we pay taxes? The answer is that the government needs money for many things, for example to pay its army, to build public facilities and to buy goods from abroad, and only the people of the country can supply the money. One of the most important taxes is income tax which a person pays according to the amount of his income. Whether he is a merchant, a doctor, a lawyer, a shopkeeper, a miner, or anything else, he must pay tax if his income is more than a certain amount. This is called a “direct”tax, because it is paid in money direct to the government. Another tax is paid on goods such as watches, jewelry, tobacco, wine, etc. When they are brought into a country, such a tax is paid as part of the price of these goods if they are later sold in shops. We call it “indirect”tax, because it is paid indirectly through the shopkeeper. People usually complain about having to pay taxes, but they forget that the money is spent on things that they and their families need. We need policemen to catch thieves, and they must be paid what they earn; children need education and there must be schools and teachers; we want our streets to be kept clean, and the wages of men who do this kind of work have to be paid. Above all, the country must always be ready to defend itself against attacking enemies, and we cannot have an army without paying for it. Taxes, therefore, cannot be avoided. We have no real cause to complain when we are asked to pay taxes for the good of ourselves and for our fellow citizens. 1. _______ Opinion We must 2.           The government needs money for many things. The money 3.           the citizens of the country. Tax sources Kinds of tax Taxpayers 4.           a person who gets income “indirect” tax 5.           6.          to pay policemen to build schools and to 7.           to pay workers 8.           to pay 9.           10.           Taxes cannot be avoided.