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问题 选择题

一个做直线运动的物体，在t = 5s内速度从v0 = 12m/s，增加到v= 18m/s，通过的位移是x = 70m，这个物体5s内的平均速度是  ( )

A．14m/s

B．15m/s

C．6m/s

D．无法确定

答案

答案：A

题目分析：平均速度因此平均速度为14m/s。答案为A。题目中的其他速度指的是某时刻的瞬时速度，并没有指明是做匀加速直线运动，因此不能被该条件迷惑而走入误区

点评：此类题型考察了平均速度的计算和理解：用位移除以时间。

选择题

如图所示，做匀速直线运动的汽车A通过一根绕过定滑轮的长绳吊起一重物B，设重物和汽车的速度的大小分别为VB、VA，则 ：

A．vA = vB

B．vA > vB

C．vA < vB

D．重物B的速度逐渐增大
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单项选择题

Observe that for the programmer，as for the chef,the urgency of the patron(顾客) may govern the scheduled completion of the task，but it cannot govern the actual completion．An omelette(煎鸡蛋)，promised in two minutes，may appear to be progressing nicely．But when it has not set in two minutes，the customer has two choices—waits or eats it raw．Software customers have had (71) choices．

Now I do not think software (72) have less inherent courage and firmness than chefs，nor than other engineering managers．But false (73) to match the patron’s desired date is much more common in our discipline than elsewhere in engineering．It is very (74) to make a vigorous，plausible，and job risking defense of an estimate that is derived by no quantitative method，supported by little data，and certified chiefly by the hunches of the managers．

Clearly two solutions are needed．We need to develop and publicize productivity figures，bug-incidence figures，estimating rules，and so on．The whole profession can only profit from (75) such data．Until estimating is on a sounder basis，individual managers will need to stiffen their backbones and defend their estimates with the assurance that their poor hunches are better than wish derived estimates．

（74）处填（）。

A．easy

B．difficult

C．simple

D．painless
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