问题 选择题

一本书放在水平桌面上静止(  )

A.书对桌面的压力就是书受的重力

B.书对桌面的压力,施力物体是地球

C.书对桌面的压力在数值上等于它受的重力

D.以上说法都不对

答案

A、书对桌面的压力与书受的重力性质不同,施力物体与受力物体也不同,所以不能说书对桌面的压力就是书受的重力.故A错误.

    B、书对桌面的压力,施力物体是书,不是地球.故B错误.

    C、书放在水平桌面上静止时,书受到重力和桌面的支持力二力平衡大小相等,根据牛顿第三定律得知,书对桌面的压力和桌面对书的支持力大小相等,所以书对桌面的压力与它受的重力大小相等.故C正确.

    D、由上得知D错误.

故选C

填空题
单项选择题

When Dave was eighteen, he bought a secondhand car for 200 so that he could travel to and from work more (1) than by bus. It worked quite well for a few years, but then it got so old, and it was costing him (2) much in repairs that he decided that he had better (3) it.

He asked among his friends to see if anyone was particularly (4) to buy a cheap car, but they all knew that it was falling to pieces, so (5) of them had any desire to buy it. Dave’s friend Sam saw that he was (6) when they met one evening, and said, "What’s (7) , Dave"

Dave told him, and Sam answered, "Well, what about advertising it in the paper You may (8) more for it that way than the cost of the advertisement!" Thinking that Sam’s (9) was sensible, he put an advertisement in an evening paper, which read "For sale: small car, (10) very little petrol, only two owners. Bargain at 50. " For two days after the advertisement first appeared, there was no (11) . But then on Saturday evening he had an enquiry. A man rang up and said he would like to (12) him about the car. "All right, " Dave said, feeling happy. He asked the man whether ten o’clock the next morning would be (13) or not. "Fine, " the man said, "and I’ll (14) my wife. We intend to go for a ride in it to (15) it. "

The next morning, at a quarter to ten, Dave parked the car in the square outside his front door, (16) to wait there for the people who had (17) his advertisement. Even Dave had to (18) that the car really looked like a wreck. Then, soon after he had got the car as clean (19) it could be, a police car stopped just behind him and a policeman got out. He looked at Dave’s car and then said, "Have you reported this (20) to us yet, sir\

18()

A.forget 

B.show 

C.disagree 

D.admit