本區搜索:
Yahoo!字典
打印

[Phy] 關於Force and Motion 的一題(Moment)

[隱藏]

關於Force and Motion 的一題(Moment)

https://drive.google.com/open?id=0B3Rm47aTiydMYWJrSWN3bjR5MUU
a)The vehicles stop in front of a traffic light. Find the tension in the cable and the nomal reaction acting on the car by the road.

應該點做?
   

TOP

you may take moment at Q
so that
clockwise moment by tension = anti-clockwise moment by weight
T sin60 * 2.3 = 9000 * 0.7

then u can use Fnet = 0 in vertical direction to find R

TOP

回覆 2# yeungwk91 的帖子

關於個tension,我都係咁計,但係個ans係3520N
而咁計出黎個ans係3163N...

TOP

回覆 3# ken759 的帖子

我以為應該有friction
有friction 嘅話 上邊咁計係無錯 =>ans錯

如果無friction
Fnet=/=0
本身架車is not in equilibrium
DSE唔會出Fnet=/=0嘅用moment 計force問題
姐係out- C
如果你都想計,就要係center of gravity take moment

TOP

Sorry
我take少左 Tcos() 嗰個anticlockwise moment

你check check條數

將Tension拆左水平同垂直之後
兩個component都會有momemt

TOP

回覆 5# yeungwk91 的帖子

可唔可以解釋下點解水平嗰個force係anticlockwise?? 好似冇乜關係  

TOP

同埋當架車moving at a constant velocity,係咪因為冇aceleration-->冇net force
個friction同Tcos60 抵消,所以冇net moment
所以架車係in equilibrium?

TOP

回覆 7# ken759 的帖子

同埋當架車moving at a constant velocity,係咪因為冇aceleration-->冇net force

It just said it stop, => probably at rest

個friction同Tcos60 抵消,所以冇net moment

Force can balance or 抵消,but the friction and tension act at different position
so
horizontal component of tension 's moment = T// * 0.4
friction moment = f * 0 = 0 since the perpendicular distance from Q = 0 (or friction passes through Q)

所以架車係in equilibrium?
Probably

TOP

引用:
原帖由 ken759 於 2016-2-21 04:21 PM 發表
https://drive.google.com/open?id=0B3Rm47aTiydMYWJrSWN3bjR5MUU
a)The vehicles stop in front of a traffic light. Find the tension in the cable and the nomal reaction acting on the car by the road.

應 ...
Take moment about Q
Anticlockwise moment = Clockwise moment
T cos (60) * 0.4 + 9000 * 0.7 = T sin (60) * 2.3
T = 3515 N ≈ 3520 N

Upward force = Downwards force
T sin 60 + R = mg
T = 5955 N ≈ 5960 N

TOP

重要聲明:小卒資訊論壇 是一個公開的學術交流及分享平台。 論壇內所有檔案及內容 都只可作學術交流之用,絕不能用商業用途。 所有會員均須對自己所發表的言論而引起的法律責任負責(包括上傳檔案或連結), 本壇並不擔保該等資料之準確性及可靠性,且概不會就因有關資料之任何不確或遺漏而引致之任何損失或 損害承擔任何責任(不論是否與侵權行為、訂立契約或其他方面有關 ) 。