1,two trains A and B are traveling on lines which cross at right angles.A travels at 40 km/h,and B at 50 km/h.find the velocity of B relative to A.2,A superman warks east at 42 km/h.He suddenly walks south at 26 km/h.What is his change in velocity gr

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1,twotrainsAandBaretravelingonlineswhichcrossatrightangles.Atravelsat40km/h,andBat50km/h.findthevelo

1,two trains A and B are traveling on lines which cross at right angles.A travels at 40 km/h,and B at 50 km/h.find the velocity of B relative to A.2,A superman warks east at 42 km/h.He suddenly walks south at 26 km/h.What is his change in velocity gr
1,two trains A and B are traveling on lines which cross at right angles.A travels at 40 km/h,and B at 50 km/h.find the velocity of B relative to A.
2,A superman warks east at 42 km/h.He suddenly walks south at 26 km/h.What is his change in velocity graw a vector diagram .
第一题，为什么这就是他们的相对速度？这道题如果是find the velocity of A relative to B 结果一样吗？
第二题望解释

1,two trains A and B are traveling on lines which cross at right angles.A travels at 40 km/h,and B at 50 km/h.find the velocity of B relative to A.2,A superman warks east at 42 km/h.He suddenly walks south at 26 km/h.What is his change in velocity gr
A相对B的速度为A的速度－B的速度.矢量减.A相对B的速度的意思是,以B为参考系,对于B来说A的速度是多少（以B的眼光来看A）.原先说的A和B的速度都是相对某个惯性系的,则若以B为参考系,原惯性系做与B的速度等大反向的运动,即原惯性系相对于B做这样的运动,而A又相对于原惯性系有速度A,则A相对于B的速度为A相对原惯性系的速度＋原惯性系相对于B的速度（即A的速度＋负B的速度,即A的速度－B的速度）.（这里说的都是矢量加减）.有很多种理解方式,关键在于惯性系的转换,要以原惯性系为媒介.其实这问题你自己想像理解,我说的只是一种理解方式.这样A相对B的速度和B相对A的速度正好等大反向.第二题速度变化量为末速度－初速度.你可以这样理解,速度的合成即为叠加,我认为宇宙中任何一个速度你都可以把它当成永远存在,只不过物体受到力的作用有加速度,产生一个新的速度,而物体原来那个速度并没有消失,而是物体即走原来那个物体的速度又走产生的新的那个速度,这就是速度的合成,即叠加,叠加后的速度即为物体现在的速度.物体初速度＋速度变化量＝物体现在的速度.这个速度变化量就是产生的那新的一个速度.

第一题，应该用A的速度减B的速度吧。补充问题应与原结果相反。
第二题，向量OA减向量OB等于向量BA，以此类推，高一数学应该学过的啊。

看图

Four years old at home,Two and a Half in Buses and Trains短文翻译 ( )The two trains go ___the tunnel___the same time.A.through;at B.across;in 1,two trains A and B are traveling on lines which cross at right angles.A travels at 40 km/h,and B at 50 km/h.find the velocity of B relative to A.2,A superman warks east at 42 km/h.He suddenly walks south at 26 km/h.What is his change in velocity gr 将A栏与B栏中选项配对,并用被动语态现在时写句子七点半前要 1 milk a (found)in france and japan2 fast trains b (cover)in snow for most of the year3 english c(divide)into two groups4the students d(produce)by cows5mount fuji in j Is your father good at ( )toy trains?A.making B.to make C.makes D.A and B 一道英语题 People travel there_____ special trains and buses. A. in B. on C. by D.take 这道题选什么 If you don't want ____ of those two trains,there is ___ one at 10:30.A.either...another B.either...the other为什么不能选B? 1:There are only three basketball teachers in our club.And we need( )A.two more B.two another C.other two D.more two He has been there for__A two and a half month B two and a half months C two and the half months D two and half a month Trains are more and more comfortable ( ).A.at present B.in the past C.the other day D.at that moment请给些说明. Though many extra planes and trains are used to carry passengers,traffic tools are still needed during May Day holidays.A.eagerly B.badly C.equally D.slightly --How much sugar do you want --________.A.Two kilos B.Two kilos and a half C.Two and half kilos D.Two and half a kilo Draw two lines A and B.Line B is longer. If you don’t want ______ of those two trains,there is ______ one at 10:30.A.any…another B.either…another C.both…the other D.either…another为什么选b,不选a? A:_______are the apples?B:Two and a half kilos. The huge elephent weights____.A two tons and a half B.two and a half ton C.half and two tonDtwo ton and a half what's twelve and two?It's( ) A、twenty two B、twenty-two C、twenty and two D、two twenty一楼的，twelve是十二的意思。 They are in Grade1,.1,后面填啥?A.and B.or C.too D.two