phy vector[YU]爺叫到就入la
本帖最後由 piyopiyo 於 13-1-2009 21:12 編輯For 3 non-parallel forces to be in equilibrium,they must
其中一個選擇係
There are lines of action passing through one point.
即係點[] 咁係唔係
----------------
2.
有架車係頂衝落泥
Q係前面個坡ge頂,亦可以睇成為一個circle of radius 10m ge頂部(圖中個circle係假的,條track係係Q成一個circle上部咁落去)
vertical distance between Q and R is 24m
問係R ge max speed so that the cart can complete the track safely
我咁做
mg-R=mv^2/r...max v when R = 0,,,如果唔係就會做到circular motion衝出條track
v^2=gr
KE at Q = KE at R - PE QR
1/2(100) + (24)(10) = (v^2)/2
580=v^2
v=24.1ms-1
其實呢題係mc
A.18.4B.22.4C.24.1D.26.1
但有幾個人都話做到18.4...[] 本帖最後由 aildux 於 13-1-2009 15:39 編輯
幾個人計到18.4 m s^-1系因為佢地用
2mg-R=mv^2/r
v^2=2gr
然後又計錯變成
2gr/2+24(10)=v^2
或者本來系
gr/2+24(10)=v^2/2兩邊乘2,唔記得將PE乘2, 結果變成
gr+24(10)=v^2
正確應該系
gr/2+24(10)=v^2/2
話俾佢地知咁樣系錯, 18.4 m s^-1連Q都去唔到仲點complete the track safely
去Q最少21.9 m s^-1 Static equilibrium
1. no rotation -> forces are concurrent.
2. no net force. 其實唔係好明
點解force一定要concurrent先唔會轉
好似有枝打橫ge棍,mg另外加2個non-parallel force,就算唔係act on同一點但都可以透過調較force ge位置做到equilibrium wor[] 其實唔係好明
點解force一定要concurrent先唔會轉
好似有枝打橫ge棍,mg另外加2個non-parallel force,就算唔係act on同一點但都可以透過調較force ge位置做到equilibrium wor[] ...
piyopiyo 發表於 13-1-2009 15:52 http://www1.nakuz.com/bbs/images/common/back.gif
e.g.? 還是我誤會了concurrent的意思?[] example plx... 見圖
mg = 100N
2邊斜上30度100N ge 力...打橫打直都無net force
2個打斜ge力同mg ge distance都一樣
咁又無moment
equilibrium[] 見圖
mg = 100N
2邊斜上30度100N ge 力...打橫打直都無net force
2個打斜ge力同mg ge distance都一樣
咁又無moment
equilibrium[]
piyopiyo 發表於 13-1-2009 17:48 http://www1.nakuz.com/bbs/images/common/back.gif
你果兩個上斜的force, direction 係相同定相反?
相同: , THEN, 應該有net force (assume mg is balanced)
相反, mg 點balance?(assume the two forces have the same magnitude)
可能我唔知你幅圖係點,因為你無比圖我-.-
都係找人答你啦,我D physics 忘記左唔少 唔記得上圖,補番