問

L.K.

急急急急急..
聽日考..
救我...
1.)轉彎果陣可以increase the normzl reaction 黎increase the max. speed
因為the frictional froce is increased..
why true???

2.)normal reaction 係N定R??

3.)

F_netradial=N-mg
點解N≠mg


4.)a small object of mass 0.05 kg is released from rest at the rim of a heavy, smooth semi-spherical boel of radius 10cm.Find the force acting on the object by the bowl when it passes the bottom of the bowl
A.0.5N    B.1.0N
C.1.5N    D.2.0N

[ 本帖最後由 L.K. 於 27-11-2008 18:41 編輯 ]

Zend

f = u R ma...

L.K.

但係我覺得INＣＲＥＡＳＥ　個ＭＡＳＳ黎ＩＮＣＲＥＡＳＥ個ＮＯＲＭＡＬ　ＲＥＡＣＴＩＯＮ唔可以ＩＮＣＲＥＡＳＥ　個ＭＡＸ　ＳＰＥＥＤ．．．　
∵friction=mv²/r
cN=mv²/r(c iscoefficient of friction)
cmg=mv²/r
v=√(cgr)

Zend

你其實個situation係點?
係平地行定banking先

兩個case 係唔同ga wor

L.K.

平地........[[tk_35]]

Zend

for question 3, 如果兩個force balance左, 那佢唔可以轉lor

N-mg = mv^2/r in this case
係top , N+mg = mv^2/r

係中間, 用conservation of energy推公式出來

normal force N 佢個力唔係constant value

L.K.

but係咩令到佢個N>mg[[tk_35]]

Zend

因為要有circular motion, 一定要某d 力provide centripetal force for circular motion

其實你gum問法, 係同問物理學家點解會有重力一樣[[tk_30]]

你都可以問, 點解centripetal force 一定要有個力pointed towards the centre acting on the object. 答案最好去宗教討論區求

L.K.

how about question 1...[[tk_35]]

Zend

你自己都prove左條式出來啦