问题 计算题

在今年5月份助残活动中,某校初三同学为伤残军人买了一辆电动轮椅。同学们对这辆车的工作原理产生了兴趣。他们对照说明书的电路原理图(如图所示)了解到,操纵杆可操纵双刀双掷开关S以及滑动变阻器R1的滑片P。前推操纵杆时轮椅前进,再向前时快速前进;拉操纵杆时,轮椅慢慢后退。又知蓄电池的电压U=24V(保持不变)、定值电阻R2=10Ω,电动机的额定功率P0=72W、额定电压U0=24V。

(1)从原理图可知,当开关S接到_________两个接线柱时,轮椅前进。

(2)当轮椅后退时,电流表示数为I=1A,此时电动机的实际功率为多少?

(3)当电动机以额定功率工作时,轮椅匀速前进的速度为1.5m/s,电动机线圈电阻损耗的功率为18W,求此时轮椅受到的阻力的大小。

答案

(1)3、4

(2)电阻R2的阻值为:U2=IR2=1A×10Ω=10V,电动机两端的电压为:U=U-U2=24V-10V=14V, 电动机的实际功率为:P=UI=14V×1A=14W;

(3)电动机的机械功率为P=P0-P线=72W-18W=54W,由于P=Fv,∴F===36N,匀速前进时:f=F=36N。

阅读理解

第三部分 阅读理解(共20小题,每小题2分,满分40分)

For many people Christmas is the most wonderful time of the year. One of the reasons people love it so much is that you get presents. But like presents, Christmas needs to be unwrapped so that you can understand the true meaning behind the day.

Many Chinese believe everyone in Western countries celebrate this holiday. That is not true. Christmas is an important religious holiday for Christians. December 25 represents the birthday of Jesus Christ, who Christians believe is the son of God.

Christianity (基督教) is a very popular religion in America and Europe. However, there are many other religions, too. People who celebrate those religions don’t celebrate Christmas. But during the winter season they usually have their own important holiday. That is why when talking to a foreigner it is safer to say, “ Happy holidays” instead of “Merry Christmas” because you never know his/her religious background.

The image of a fat, happy man in red---Santa Claus---has come to represent the idea of goodness and love instead of religious part or the “Christmas spirit”. Santa Claus is based on a man named Saint Nicholas who was a 4th century Greek Christian.

Saint Nicholas bought presents for children and gave them away anonymously(匿名地). This is where the idea of gift on Christmas began. But the Santa Claus didn’t exist until the 19th century when an American named Thomas Nast drew cartoons of him. So really, Santa has nothing to do with the religious holiday.

In fact, some people who celebrate Christmas don’t really care about Santa Claus.

Christmas is a special day for Christians but the ideas of being good and loving your neighbors are not limited to Christianity. So buy a gift for your friend, tell your mother you love her and have merry Christmas. I mean ,”Happy holidays!”

56. Christians believe December 25 represents the birthday of _________.

A. Santa Claus     B. God    C. Jesus Christ     D. Thomas Nast

57. In the passage, the author thinks __________.

A. Santa Claus was a real person in the past

B. everyone should believe in Christianity

C. all people in Western countries celebrate Christmas

D. Santa Claus has nothing to do with Christmas holiday

58. What is “the true meaning” in the first passage?

A. For many people Christmas is the most wonderful time of the year

B. The Westerners have different religious backgrounds

C. Some like to say “Merry Christmas”, and others like to say “Happy holidays”

D. Being good and loving our neighbors are the virtues of all humans

59. What is the CORRECT explanation of Santa Claus?

A. He was a Greek Christian in the 4th century

B. He was an American who was born in the 19th century

C. His image represents the “Christmas spirit”

D. He was a cartoon figure drawn by Thomas Nast

判断题