A boat has a maximun speed of 4 km per hour in still water.It is moving across a river where the speed of flow is 2 km per hour. If the captain wishes to take the shortest route (perpendicular to the stream flow ) at the maximum speed, how should he steer the boat upstream?
A) 30 degree with the stream
B) 45 degree with the stream
C) 60 degree with the stream
D) 63.4 degree with the stream
ans:C
Please teach me to do with explanation....Thank you very much !!!
al physics
2010-06-20 2:23 am
回答 (1)
2010-06-20 2:32 am
✔ 最佳答案
You can refer to the diagram below:圖片參考：http://i388.photobucket.com/albums/oo325/loyitak1990/Jun10/Crazymech1.jpg
Using the diagram, we have:
4 cos θ = 2
cos θ = 0.5
θ = 60
Hence ans = C
2010-06-19 18:33:56 補充：
Since the boat's resultant speed is perpendicular to the stream, the boat should be steered to a direction such that its velocity component in the stream's direction is 2 km/h opp. to it.
參考: Myself
收錄日期: 2021-04-13 17:19:18
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100619000051KK01083