问题 多选题

空中某点,将三个相同小球同时以相同的初速度v水平抛出、竖直上抛、竖直下抛,则从抛出到落地,设地面为零势面,忽略空气阻力,下列说法正确的是(  )

A.竖直向上抛的小球在下落过程中重力势能的变化量最大

B.三个小球落地的速度相同

C.落地时重力的瞬时功率相同,方向都是竖直向下

D.竖直下抛的小球,其重力的平均功率最大

答案

A、竖直向上抛的小球下落的高度最大,重力做功最大,其它两个小球下落高度相同,因此竖直上抛的小球在下落过程中重力势能的变化量最大,故A正确;

B、小球沿着不同的方向抛出,都只有重力做功,机械能守恒,故可得到落地时速度大小相等,但方向不同,速度不同,故B错误;

C、三个球落地时速度大小相等,根据瞬时功率表达式P=Fvcosθ,平抛运动重力的瞬时功率最小,竖直上抛与竖直下抛的小球落地时的瞬时功率相等,故C错误;

D、根据重力做功公式W=mgh可知,三个小球重力做功相同,落地的时间不同,竖直上抛时间最长,竖直下抛时间最短,所以运动过程中,三个小球重力做功的平均功率不同,下抛平均功率最大,故D正确;

故选:AD.

完形填空
What is Math Anxiety?
Math anxiety or fear of math is actually quite common. Math anxiety is quite   36 to stage-fright. Why does someone suffer   37 ? Fear of something going wrong in front of a crowd? Fear of   38 the lines? Fear of being judged   39 ? Fear of going completely blank? Math anxiety conjures(使现出) up fear of some type. The fear that one won’t be able to do the   40 or the fear that it’s too hard or the fear of failure which often stems(起因于) from having a lack of  41 . For the most part, math anxiety is the   42 about doing the math right, our minds draw a   43 and we think we’ll fail and of course the more frustrated and anxious our minds become, the  44 the chance for drawing blanks. Added pressure of having time limits on math tests and exams also cause the levels of anxiety to grow for many students.
Where Does Math Anxiety Come From?
Usually math anxiety stems(起源于) from   45 experiences in mathematics. Typically math phobias(恐慌症) have had math presented in such a fashion that it led to limited understanding. Unfortunately, math anxiety is often   46  poor teaching and poor experiences in math which typically leads to math  47 . Many of the students I’ve encountered with math anxiety have demonstrated an over reliance on procedures in math as opposed to actually understanding the math. When one tries to memorize procedures, rules and routines without much   48 , the math is quickly forgotten and   49 soon sets in. Think about your experiences with one concept — the division of fractions(分数). You probably learned about reciprocals(倒数) and inverses. In other words, ‘It’s not yours to reason why, just invert(反转) and multiply(乘)’. Well, you memorized the rule and it   50  . Why does it work? Do you really understand why it works? Did anyone ever use pizzas or math manipulative(巧妙处理的) to show you why it works? If   51  , you simply memorized the procedure and that was that. Think of math as memorizing all the procedures —   52 if you forget a few? Therefore, with this type of strategy, a good  53 will help, but, what if you don’t have a good memory. Understanding the math is critical. Once students   54 they can do the math, the whole notion of math anxiety can be overcome. Teachers and parents have an important   55 to ensure students understand the math being presented to them.
小题1:
A.different B.similar C.far D.familiar
小题2:
A.speech B.performance C.threatens D.stage-fright
小题3:
A.understanding B.memorizing C.forgetting D.reading
小题4:
A.poorly B.crazily C.well D.publicly
小题5:
A.Chinese B.math C.English D.physics
小题6:
A.wish B.conscience C.determination D.confidence
小题7:
A.fear B.joy C.pleasureD.doubt
小题8:
A.failure B.choice C.blank D.death
小题9:
A.further B.greater C.less D.smaller
小题10:
A.unpleasant B.unfair C.pleasant D.successful
小题11:
A.because B.thanks to C.resulting in D.due to
小题12:
A.fear B.anxiety C.failure D.misunderstanding
小题13:
A.forgetting B.use C.understanding D.knowledge
小题14:
A.panic B.excitement C.disappointment D.encouragement
小题15:
A.opens B.works C.starts D.runs
小题16:
A.so B.possible C.not D.any
小题17:
A.Where B.Why C.When D.What
小题18:
A.memory B.method C.brain D.body
小题19:
A.fill B.realize C.confirm D.recognize
小题20:
A.task B.aim C.appointment D.role
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