试题与答案

甲、乙两物体在同一地点分别从4h和h高处开始做自由落体运动,已知甲物体的质量是乙

题型:选择题

题目:

甲、乙两物体在同一地点分别从4h和h高处开始做自由落体运动,已知甲物体的质量是乙物体的4倍,下列说法正确的是(  )

A.落地时,甲和乙的速度相等

B.落地时,甲的速度是乙的速度的2倍

C.甲、乙同时落地

D.甲的下落时间是乙的下落时间的4倍

答案:

A、由于高度不同,则有v2=2gh可知,落地时速度不相等,故A错误;

B、由v2=2gh得v=

2gh
,故速度与
h
成正比,故甲的速度是乙的速度的2倍;故B正确;

C、因高度不同,则下落时间不同,故C错误;

D、由h=

1
2
gt2可得,t=
2h
g
,故时间与
h
成正比,故时间之比为2:1,即甲的下落时间为乙的下落时间的2倍,故D错误;

故选:B.

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A. Japan

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C. India

D. Holland

3. In _____, only birthday children wear colored clothes to school.

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A. 15

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C. 5

D. 3

5. The passage is mainly about _____.

A. similar ways of celebrating birthdays in some countries

B. different ways of celebrating birthdays in some countries

C. children's birthdays in western countries

D. the importance of children's birthdays

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