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[Geog] 地理mc#01#25

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地理mc#01#25

點解ans係a 唔係b- -?

[ 本帖最後由 j神 於 2010-4-14 12:46 PM 編輯 ]
   

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引用:
原帖由 j神 於 2010-4-14 11:45 AM 發表
點解ans係a 唔係b- -?
ok ... here is the question:


Apparently, as shown in your doubt, you know the possible answers should be A or B, since the first dominating factor that affecting the velocity of a river is the wetted perimeter ... and that's why for C and D, the longer the wetted perimeter, the greater the friction, the lower the velocity of the river.

However, in this question, the key-concept is,
the effect of the area of the river cross-section is greater than the effect of the wetted perimeter.

As you can see, for option A, due to the shape of the river channel is more deepened that than of B. Therefore, even though the wetted perimeter of B is shorter, the average volume of water-flow of it is still less than A.

and you should probably know, not to mention about gradient, the volume of water-flow is also a factor that is positively related to velocity.

Hence, you should now know that, the amount of friction casued in river A should be relatively smaller than B.In this way,
the smaller the friction, the higher the velocity of the river.

KELY TO, a F.6 student who are quite interested in geography.

P.S. Should you have any enquiries or comments, or suggestions, please feel free to contact me.
MSN: kely_to@hotmail.com




[ 本帖最後由 kely_to 於 2010-4-14 01:38 PM 編輯 ]
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