问题 选择题

如图所示为大型电子地磅电路图,电源电动势为E,内阻不计.滑动变阻器上A、B间距离为L,最大阻值等于定值电阻的阻值R0,弹簧下端固定,上端与托盘相连.不称物体时,滑片P在A端,称重物时,在压力作用下使滑片P下滑,这样通过电流的大小可以知道物体的重量,把电流对应的重量值刻在刻度盘上.若已知弹簧的总弹力与形变量成正比,比例系数为k,所称重物的重量G与电流大小I的关系为(  )

A.G=(2-

E
IR0
)kL

B.G=(

E
IR0
-1)kL

C.G=(

E
IR0
+1)kL

D.G=kIL

答案

由胡克定律可知,Kx=G;

得:x=

G
K

此时滑动变阻器接入电阻R′=

L-x
L
R0=
L-
G
K
L
R
0

由闭合电路欧姆定律可知:I=

E
R0+R′

解得:G=(2-

E
IR0
)kL

故选A.

完形填空

第二节:根据短文内容,从A、B、C、D、E中选出最适合放入短文空缺处的选项,并将序号及相应答案写在答题纸上。选项中有一项是多余选项。

Jogging (慢跑) is basically running at a steady (平稳的) speed over short or long distances. It has become popular some twenty years and remained a favorite way of keeping fit for lots of people.

65    People jog around college campuses, in parks, in the countryside and even in urban areas. Special courts, fields and running tracks are not necessary. Similarly, no special equipment is required — no costly hats, or balls, and no expensive sports kit. Good quality running shoes are advisable, but otherwise the jogger can simply wear loose, comfortable clothing.

66    It’s not unusual to see joggers exercising in the height of summer or in the depth of winter! Jogging is a solo (单独的) sport. You don’t need to wait until you have formed a team or found a partner. You can jog alone. A few words of warning, however: lone female joggers should be especially careful to choose sensible jogging routes, particularly at night time.

67    You just need to be basically healthy and after basic warming up, you are ready to begin. You simply start running, gently, and then build up to a steady pace. Do not overtire yourself by trying to go too fast. A steady, comfortable pace is your aim.

68    It’s good for the lungs, the heart and the circulation (循环). It’s easy and it’s convenient. Why don’t you try it? If you require more information, talk to one of the instructors at the sports centre. We are only too happy to help. Please remember: if you do decide to jog, talk to your doctor first if you have any health worries. Happy jogging!

A. Jogging is excellent for keeping fit.

B. That’s the reason why people like jogging.

C. The act of jogging doesn’t need any special training or skill.

D. One of the main advantages of jogging is that it can be done anywhere.

E. In addition to being able to jog anywhere, you can also jog at any time, in any season!

选择题