问题 选择题

用一轻绳将小球P系于光滑墙壁上的O点,在墙壁和球P之间夹有一矩形物块Q,如图所示。P、Q均处于静止状态,则下列相关说法正确的是(     )

A.P物体受4个力

B.Q受到3个力

C.若绳子变长,绳子的拉力将变小

D.若绳子变短,Q受到的静摩擦力将增大

答案

AC

题目分析:A、对P进行受力分析,P受重力、绳子拉力,Q对P的支持力,由于墙壁光滑,Q静止说明P对Q有向上的摩擦力,Q对P有向下的摩擦力,所以P受4个力;正确

B、Q受重力,P对Q的摩擦力,P对Q的压力,墙壁对Q的支持力共4个力;错误

C、设绳子与墙壁夹角为θ,对P进行受力分析得,若绳子变长,θ变小可得F变小;正确

D、由于Q处于静止状态,根据二力平衡可得Q受到的静摩擦力等于Q的重力,Q受到的静摩擦力不变;错误

故选AC

点评:对于处于平衡状态的物体,受力一定平衡,根据这一点就可以分析出一些无法判断有无得力。

完形填空
If you asked high school girls to name their favorite sports, most would probably say basketball or volleyball. I happen to be one of the few girls who would  36 :surfing. But isn’t that a boy thing? Some people  37 .Most certainly not.
I started surfing about five years ago and 38 in love with the sport on the very first day. Riding that first  39  was the best feeling I had ever experienced.
When I try to  40  surfing with other things, I find it very difficult because, in my ___41_ ,there’s nothing like it. It involves body, 42 ,and soul. There’s sand between my toes and cool, salt water all  43  us. The feeling I get when I’m surfing across that  44 ,becoming one with the  45 ,is like I’m weightless.
The one thing I can  46  from surfing and not any other sport is endless challenge. You can never be the “best surfer” because the ocean  47  an uncountable variety of waves that nobody can ever master. The variations of surfing styles are wonderful. Some surfers are free and flowing; others are very aggressive and  48 .All of these things attract me to surfing and make it  49   from any other sport.
I’ve  50  to tell every girl I know to do something that people don’t think girls can do. It’s part of being human to advance to new  51 ,so shouldn’t it be expected that girls should step up and start  52  the limits of things boys and men used to dominate?
There’re women  53  side by side with the President of our country, so why not side by side with the boys  54  the football team or out in the water surfing? Give girls a chance to __55 , and they will.
小题1:
A.tell   B.answer  C.give   D.realize
小题2:
A.wonderB.understandC.replyD.believe
小题3:
A.stayedB.cameC.droppedD.fell
小题4:
A.waveB.stormC.sailD.boat
小题5:
A.bringB.connectC.compareD.tie
小题6:
A.workB.studyC.holidayD.life
小题7:
A.mindB.effortC.healthD.time
小题8:
A.alongB.aboveC.aroundD.by
小题9:
A.beachB.waterC.boardD.lake
小题10:
A.skyB.worldC.earthD.ocean
小题11:
A.takeB.getC.makeD.keep
小题12:
A.catchesB.includes C.offers D.collects
小题13:
A.sharpB.greatC.hard D.calm
小题14:
A.knownB.rightC.farD.different
小题15:
A.chosenB.triedC.learnedD.promised
小题16:
A.levelsB.pointsC.stepsD.parts
小题17:
A.reachingB.acceptingC.pushingD.setting
小题18:
A.sittingB.walkingC.fightingD.working
小题19:
A.ofB.from C.onD.with
小题20:
A.thinkB.succeedC.performD.feel
问答题 简答题