问题 问答题

如图所示,光滑斜面的倾角为θ=37°,可以看成质点的某物体的质量为m,物体从距离水平面高为h=1.8m的A点由静止开始沿斜面下滑,经过B点后进入粗糙的水平地面(设物体经过B点时速度的大小不变),最后停在C点,已知物体与水平地面的动摩擦因数为μ=0.2,试求出物体到达B点时的速度大小vB和B、C两点间的距离s.(已知sin37°=0.6,g=10m/s2

答案

在斜面上对物体受力分析,如图所示,设物体在斜面上的加速度大小为a1

根据牛顿第二定律得,mgsinθ=ma1

解得a1=gsinθ=6m/s2

下滑的位移s1=

h
sinθ
=3m

所以vB=

2as1
=6m/s.

在粗糙水平面上对物体受力分析,如图所示,设物体的加速度大小为a2

则f=μN=ma2

N′=mg

解得a2=μg=2m/s2

所以s=

vB2
2a2
=9m.

答:物体到达B点时的速度大小为6m/s,B、C两点间的距离为9m.

填空题
阅读理解

阅读理解。

     TOKYO-A child-like robot that combines the roles of nurse,companion and security guard

is to go on the market to help the growing ranks of elderly Japanese with no one to look after

them.

      The "Wakamaru" robot can walk around a house 24 hours a day,warning family,hospitals

and security firms if it perceives(notices)a problem.It will,for example,call relatives if the owner

fails to get out of the bath.

     Cameras implanted in the "eye-brows" of the robot enable it to "see" as it walks around an

apartment.The images can be sent to the latest cell phones,which display the pictures.

      Mitsubishi Heavy Industries which developed Wakamaru plans to start selling the meter-high

robots for about $15 000.

     Wakamaru,which speaks with either the voice of a boy or girl,is also designed to provide

companionship,greeting its "papa" when he comes home.

     It is the first household robot able to hold simple conversations,based on a vocabulary of

around 10 000 words.It cannot only speak but can understand answers and react accordingly.

     It will ask "Are you all right?" if its owner does not move for some time.If the answer is no,

or there is no answer,it will telephone preset numbers,transmitting images and functioning as a

speakerphone.

     Wakamaru will inform a security firm if there is a loud bang or if an unknown person enters

the house while the owner is out or asleep.It can recognize up to 10 faces . But like most robots

it cannot climb stairs.

     It can be set to remind forgetful people when it is time to take medicine,eat and sleep.

      Mitsubishi adapted Wakamaru from robots which already makes to go around nuclear power

facilities(设施).The idea to use the technology in the home came from a company employee.

     The project chief said:"Looking at the ageing of society and the falling birth rate we decide that

this could work as a business.We want to offer Wakamaru as a product that helps society.

     The technology has gained nation-wide publicity in Japan among increasing concern over how

to look after the ever-growing number of old people.The life expectancy of Japanese women has

shot up to almost 85,the highest in the world.

      At the same time,extended families are being replaced by nuclear families.This has left many

Japanese anxious about their elderly parents,whom they rarely see because of their long hours at

the office.

1.Which of the following is TRUE about the Robot?

A.It is used in some nuclear power facilities.

B.It cannot speak but can understand answers.

C.It can go up and down the stairs easily.

D.It can recognize as many as 10 faces.

2.The purpose of this passage is __________.

A.to introduce a new product

B.to solve the ageing problems

C.to tell people how to use the robot

D.to show the rapid development of technology

3.What can we infer from the passage

A.The robot can dial proper numbers for help.

B.The robot is likely to have a promising market.

C.The robot has given the Japanese a chance to live longer.

D.The nuclear families have left many elderly Japanese anxious.

4.What is the best title of this passage

A.The Latest Development of Robot Technology

B.Japanese Robot and the Ageing Society

C.Vast Market of the New Robot

D.Japanese-built Robot to Help the Old