问题 实验题

(4分)在“验证力的平行四边形定则”实验中,需要将橡皮条的一端固定在水平木板上,另一端系上两根细绳,细绳的另一端都有绳套(如图)。实验中需用两个弹簧秤分别勾住绳套,并互成角度地拉橡皮条。某同学认为在此过程中必须注意以下几项:

A.两根细绳必须等长。

B.橡皮条应与两绳夹角的平分线在同一直线上。

C.在使用弹簧秤时要注意使弹簧秤与木板平面平行。

D.弹簧秤不能接触水平木板。

其中正确的是______。(填入相应的字母) 

答案

C D

题目分析:该实验验证两个分力的效果和其合力的效果相同,与两根绳是否等长无关,橡皮条也不必与两绳夹角的平分线在同一直线上;在使用弹簧秤时要注意使弹簧秤与木板平面平行,以及弹簧秤不能接触水平木板,可以减小实验时的误差,正确选项为C、D。

阅读理解

.

Commercial (商业广告) business is profitable (有利可图的),and most radio and TV stations depend on the income.  The prices for radio and TV commercials are different according to the popularity (声望) of the station and the time they give. Take WGY, a rock music station in Albary, New York, for instance, they ask $100 for a one-minute commercial from 6 a.m. to 10 a.m., the morning driving time. This is a time when people are driving on their way to work and they like to turn on their car-radios.

During other hours of the day the cost varies (变化) from $25 to $60 for one minute. TV commercials are much more expensive. During a good national or international football game or baseball game, the price for a one-minute TV commercial may reach as high as $100,000. On local TV station, prices of commercials are different according to the different programmes and the time of showing. At 7 p.m., when the TV stations are showing their most popular programmes, the price for a commercial for 30 seconds is $800.

49. This passage mainly tells that ________.

A. WGY, a rock music station earns much money by broadcasting commercials

B. the prices for commercials are different according to the different programmes

C. TV commercials are much more expensive than radio ones

D. commercial business can help most radio and TV stations earn a lot of money

50. The prices for radio and TV stations depend mainly on _______.

A. different radio and TV stations

B. different time the commercials are given

C. the most popular programmes

D. all of the above

51. How much does WGY, a rock music station ask for a half minute commercial at 9 a.m.?

A. $25                          B. $50                          C. $60                          D. $100

52. When a commercial is shown at 7 a.m. on the local TV station for one minute, it will cost ________.

A. eight hundred dollars                                     B. eighty hundred dollars

C. sixteen hundred dollars                                  D. sixty hundred dollars

单项选择题