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2c細成二轉會員
2009-4-18 10:43#1
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無聊的＊晶＊三星高級會員
2009-4-18 20:58#2
(c):Mgsin30>F, so we need a force P to prevent the block from moving downward...
So,F+P=Mgsin30,F & P must in the same direction....
I think...
If we remove P,Mgsin30 and friction are in opposite direction and the block will move downward, so friction and mgsin30 must in opposite direction...
I'm not sure at all,i'm not高手...
[ 本帖最後由 無聊的＊晶＊ 於 2009-4-18 09:03 PM 編輯 ]
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Why?VIP會員
2009-4-19 01:26#3
個block向下行嘛, 咁咪有個向下既force act on 個plane
咁個plane咪比番向上既reaction force(friction)頂番住佢
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紫魂傲=]五星白金會員
2009-4-19 17:58#4
P+F岩岩好夠prevent佢moving down 唔洗再用額外既力
