回复:回复:我请教一个高小的题吧。

来源: acorntechusa 2011-02-03 21:58:18 [] [博客] [旧帖] [给我悄悄话] 本文已被阅读: 次 (299 bytes)
回答: 回复:我请教一个高小的题吧。acorntechusa2011-02-03 21:53:08

swimming along the 30 degree angle,1m/s * tan(30) = 0.5m/s.  This will keep the dog always smim straight forward toward opposite B point.  The net speed to swim cross the river is 1m/s * tan(60) = 0.86605 m/s.  Rive width 20m: t = 20/0.86605 = 23s

 

 

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回复:Agree. Net speed of dog and river flow is sqrt(3)/2 -Yangtze430030- 给 Yangtze430030 发送悄悄话 Yangtze430030 的博客首页 (0 bytes) () 02/04/2011 postreply 09:23:01

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