问题 计算题

科研人员乘气球进行科学考察,气球、座舱、压舱物和科研人员的总质量为990kg。气球在空中停留一段 时间后,发现气球漏气而下降,及时堵住,堵住时气球下降速度为1m/s,且做匀加速运动,4s内下降了 12m。为使气球安全着陆,向舱外缓慢抛出一定的压舱物。此后发现气球做匀减速运动,下降速度在5分钟内减少3m/s。若空气阻力和泄漏气体的质量均可忽略,重力加速度g=9.89m/s2,求抛掉的压舱物的质量。

答案

解:由牛顿第二定律得:mg-F=ma,

抛物后减速下降有:F-(m-m')g=(m-m')a',△v=a'△t

解得

阅读理解

阅读理解

    Suppose you work in a big firm and find English very important for your job because you often deal with foreign businessmen.Now you are looking for a place where you can improve your English,espeually your spoken English.

     Here are some information you need about English Language training.

     Global English Centre

    *General English in all four skills listening,speaking,reading and writing *3-month(700 yuan),6-month(1,200 yuan)and one-year(2,000 yuan) courses *Choice of morning or evening classes,3 hours per day,

Mon-Fri *Experienced college English teachers. *Close to city centre and bus stops. Tel:67605272  

Add:105 Zhongshan Road,100082  

     Modern Language School *Special courses in English for business,travel,banking,hotel management and office skills. *Small classes(12-16 students)on Sat,& Sun,from 2:00-5:00pm. *Native English teachers

from Canada and USA. *Language lab and computers supplied. *3-month course:1,050 yuan;6-month

course:1,850 yuan. Write or phone:Modern Language School,675 Park Road 100056 Tel:67353019

     The 2lst Century English Training Centre *We specialize in effective teaching at all levels. *We offer

morning or afternoon classes,both of which last three months and a half at a cost of 800 yuan. *We also

have a six-week TOEFL preparation class during winter and summer holidays. *Entrance exams:June 1

and Dec 1 *Only 15-minute walk from city centre. Call 67801642 for more information

    The International House of English *Three/Six-month English courses for students of all levels at very

cost:60 yuan for 12 hours per week;convenient class hours:9:00-12:00am and 2:00-5:00pm. *A four-

month evening programme for developing speaking skills(same cost as day classes) *Well-trained Chinese and foreign teachers experienced in teaching English as a second/foreign language. *Free sightseeing and

social activities(活动) *Very close to the Central Park. For further information call 67432308

1.You work from 9:00am to 4:30pm every day which schools will you choose?

A.Global English Centred and the International House.

B.Global English Centre and Modern Language School.

C.Modern Language School and the 21st Century.

D.The 21st Century and the International House

2.The 21st Century is different from the other three schools in that____.

A.its teaching quality is better

B.it is nearest to the city centre

C.it requires an entrance examination

D.its courses are more advanced

3.You will probably prefer to go to the International House because it____.

A.offers free sightseeing and social activities

B.costs less than the other schools

C.has a special course in spoken English

D.has native English teachers

4.If you take the evening programme at the International House,you will pay about___

A.60 yuan

B.240 yuan

C.730 yuan

D.1000 yuan

5.The passage is most probably taken from_____.

A.travel book

B.a library guide

C.advertisements from newspapers

D.a project handbook

单项选择题