关于质点的位移和路程，下列说法正确的是
A．物体通过的路程不等于零,其位移也一定不等于零
B．位移的大小不会比路程大
C．路程是标量，即位移的大小
D．当质点做直线运动时，路程等于位移的大小
答案：B
A. 物体的位移只与初末位置有关,与物体的实际路径无关,只要物体回到初始点,位移就为零；
B. 位移的大小始终小于等于路程；
C. 路程是标量，是物体实际运动轨迹的长度；
D. 只有物体做单方向的直线运动时，路程等于位移的大小。
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| Sometimes I really doubt whether there is love between my parents.They are very busy working to _1 the family.They don't act in the _2_ ways that I read in books or I see on TV._3_ flowers to each other on Valentine's Day is even more _4_. One day,my mother was sewing a quilt (床罩).I _5_ sat down beside her and looked at her."Mom,is there love between you and Dad?" I asked her in a _6_ voice. My mother stopped and raised her head with _7_ in her eyes.She didn't answer immediately.Then she _8_ her head and continued to sew the quilt.At last my mother said: "Susan," she said,"Look at this thread.Sometimes it appears,but most of it _9_ in the quilt.The thread really makes the quilt strong and _10_.If life is a quilt,then love should be a _11_.It can hardly be seen anywhere or anytime,but it's really there.Love is _12_." The next spring,my father suddenly got sick seriously.When they returned from the hospital,mother looked rather pale and it seemed _13_ of them had had a serious illness.Every day in the morning and dusk,my mother helped my father _14 slowly on the country road.My father had never been so _15_. Along the country road,there were many beautiful flowers,green grass and trees.The sun gently glistened through the leaves.All of these _16_ the most beautiful picture in the world. "Dad,how are you feeling now?" I asked him one day. He said gently."_17_,I just like walking with your mom.I like this kind of life." _18_ his eyes,I know he loves my mother deeply. _19_ I thought love meant flowers,gifts and sweet kisses.But from this _20_,I understand that love is just a thread in the quilt of our life.Love is inside,making life strong and warm. | ||||
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