某同学前后两次从同一位置水平投出两支飞镖1和飞镖2到靶盘上，飞镖落到靶盘上的位置如图所示，忽略空气阻力，则两支飞镖在飞行过程中：（ ）
A．飞行时间t1＜t2
B．角度θ1＞θ2
C．加速度a1＞a2
D．初速度v1=v2
飞镖1下落的高度小，根据h=
gt2，t=1 2
知，t1＜t2．2h g
由于水平位移相等，根据x=v0t，知v1＞v2．
加速度相等，都为g．
根据tanθ=
=v0 vy
，对于飞镖1，时间短，初速度大，则tanθ1＞tanθ2，所以θ1＞θ2．故A、B、D正确，C错误．v0 gt
故选ABD．
| 完形填空。 | |||
| For many people today,reading is no longer relaxation.To keep up their work they must read letters,reports,trade publications,interoffice communications,not to mention newspapers and magazines;a never-ending flood of words.In 1 a job or advancing in one,the ability to read and comprehend 2 can mean the difference between success and failure.Yet the unfortunate fact is that most of us are 3 readers.Most of us develop poor reading 4 at an early age,and never get over them.The main deficiency(缺陷)5 in the actual stuff of language itself-words.Taken individually,words have 6 meaning until they are strung together into phrases,sentences and paragraphs.7 however,the untrained reader does not read groups of words.He laboriously reads one word at a time,often regressing to 8 words or passages.Regression,the tendency to look back over 9 you have just read,is a common bad habit in reading.Another habit which 10 down the speed of reading is vocalization-sounding each word either orally or mentally as 11 reads. To overcome these bad habits,some reading clinics use a device called an 12,which moves a bar(or curtain)down the page at a predetermined speed.The bar is set at a slightly faster rate 13 the reader finds comfortable,in order to "stretch" him.The accelerator forces the reader to read fast,14 word-by-word reading,regression and subvocalization,practically impossible.At first 15 is sacrificed for speed.But when you learn to read ideas and concepts you will not only read faster,16 your comprehension will improve.Many people have found 17 reading skill greatly improved after some training.18 Chalice Au,a business manager,for instance,his reading rate was a reasonably good 172 words a minute 19 the training,now it is an excellent 1378 words a minute.He is delighted that how he can 20 a lot more reading materials in a short period of time. | |||
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