问题 多选题

小物块在t=0时刻以初速度v0自固定斜面的底端上滑,设斜面足够长,取v0方向为正方向,则关于物块的速度-时间图象,下列图中可能的是(  )

A.

B.

C.

D.

答案

A、当μmgcosθ>mgsinθ时,物体滑动斜面的顶端后保持静止.故A正确.

B、当斜面粗糙时,物体在斜面上滑行时受到的滑动摩擦力大小:f=μFN

而:FN=μmgcosθ

所以物体沿斜面向上滑行时有:mgsinθ+f=ma1

故物体沿斜面向上滑行时的加速度:a1=gsinθ+μgcosθ

物体沿斜面向下滑行时有:mgsinθ-f=ma2

所以物体沿斜面向下滑行时的加速度:a2=gsinθ-μgcosθ

故a1>a2,所以B正确.

C、当斜面光滑时:μ=0,

故有:a1=a2=gsinθ,故C正确.

D、物体不可能先匀减速上升再匀加速上升的.故D错误.

故选ABC.

完形填空

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多于选项。

Public Speaking Training

·Get a coach

     小题1:     ,so get help. Since there are about a billion companies out there all ready to offer you public speaking training and courses, here are some things to look for when deciding the training that's right for you.

·Focus on positives

Any training you do to become more effective at public speaking should always focus on the positive aspects of what you already do well. Nothing can hurt confidence more than being told that you aren't doing well.    小题2:    , so good public speaking training should develop those instead of telling you what you shouldn't do.

If you find a public speaking course that looks as though it's going to give you lots of dos and don'ts, 小题3:walk away! Your brain is so full of what you're going to be talking about.

  小题4:   . As far as we're concerned, there are basically no hard and fast rules about public speaking. Your audience can be your friends.

·You are a special person not a clone

Most importantly, good public speaking training should treat you as a special one, with your own personal habits.      小题5:     . Your training course should help you bring out your personality, not try to turn you into someone you're not.

A.You aren't like anybody else

B.You already do lots of things well

C.Turn your back on too many rules

D.Check the rules about dos and don'tsE. Whatever the presentation, public speaking is tough

F .The one thing you don't want is for them to fall asleep

G. So trying to force a whole set of rules into it will just make things worse

判断题