查看完整版本 : 兩小題phy mechanics MC!!!

dicky821 2012-7-3 12:54 PM

兩小題phy mechanics MC!!!

向各位CHING 求救...!! :funk:
呢題應該點做???
我幅free body diagram又畫得岩唔岩??:smile_41:
[img]http://i1126.photobucket.com/albums/l617/dicky821/phy-2.jpg[/img]

仲有一題!!!
[img]http://i1126.photobucket.com/albums/l617/dicky821/PHY2.jpg[/img]

[[i] 本帖最後由 dicky821 於 2012-7-3 02:53 PM 編輯 [/i]]

14c14c 2012-7-3 09:20 PM

1.A
2.A??

nannanzhang 2012-7-4 05:30 PM

你個free-body diagram好似錯左。你向上最大力抗衡時, 個f 會向下, so fmax = 11 - mg sin theta, 之後會冇了 F, f 會指返去斜上, 會hold住個block 唔俾佢跌, 所以係 A:smile_14:
有錯請修正

Anthonyhin 2012-7-7 10:28 PM

下面個條係B:smile_44:

dicky821 2012-7-8 03:11 PM

[quote]原帖由 [i]Anthonyhin[/i] 於 2012-7-7 10:28 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=334931978&ptid=19775127][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
下面個條係B:smile_44: [/quote]
係呀ching:smile_38: 可唔可以賜教?...唔知點計:smile_27::smile_42:

Anthonyhin 2012-7-8 03:27 PM

[quote]原帖由 [i]dicky821[/i] 於 2012-7-8 03:11 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=334988887&ptid=19775127][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

係呀ching:smile_38: 可唔可以賜教?...唔知點計:smile_27::smile_42: [/quote]
拆力 W = 2T cos角



[url=http://www.discuss.com.hk/iphone][img=100,23]http://i.discuss.com.hk/d/images/r10/iphoneD.jpg[/img][/url]

Anthonyhin 2012-7-8 03:30 PM

[quote]原帖由 [i]Anthonyhin[/i] 於 2012-7-8 03:27 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=334990159&ptid=19775127][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

拆力 W= 2T cos
所以W 一定大過T
所以b
[/quote]



[url=http://www.discuss.com.hk/iphone][img=100,23]http://i.discuss.com.hk/d/images/r10/iphoneD.jpg[/img][/url]

14c14c 2012-7-8 05:01 PM

一考完AL就成日計錯數:smile_27:
W=2Tcos(theta)
for 0< theta<90
0<cos(theta)<1
0<2Tcos(theta)<2T
W<2T
T>W/2

for theta <60
cos (theta) >1/2
2Tcos(theta) > T
W>T

therefore W>T>W/2

Anthonyhin 2012-7-8 10:26 PM

friction 應該係oppose the motion
同埋你差左個weight

14c14c 2012-7-8 11:02 PM

[quote]原帖由 [i]Anthonyhin[/i] 於 2012-7-8 10:26 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=335029541&ptid=19775127][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
friction 應該係oppose the motion
同埋你差左個weight [/quote]
佢淨係consider parallel to the plane既 force, 因為得parallel to the plane 既方向先有motion
mg sin30已經代表左weight 係parallel to the plane 既方向既component

dicky821 2012-7-9 11:38 PM

[quote]原帖由 [i]14c14c[/i] 於 2012-7-8 11:02 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=335034736&ptid=19775127][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

佢淨係consider parallel to the plane既 force, 因為得parallel to the plane 既方向先有motion
mg sin30已經代表左weight 係parallel to the plane 既方向既component [/quote]
唔該哂CHING幫我解釋同賜教:smile_40: 完全明白哂 thx!!! :loveliness::smile_38:
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查看完整版本: 兩小題phy mechanics MC!!!