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標題: convex " mirror"?? [打印本頁]

作者: 小霞的fans 時間: 7/8/2009 06:50 PM
標題: convex " mirror"??
我淨係知咩係convex lens 冇聽過convex mirror..

an object is placed in front of a convex mirror.which of the following statements about the properties of the image formed in the mirror must be correct?

1.the image is diminished.
2.the image is virtual.
3.the image distance is smaller than the focal length of the mirror.

A.1 and 2 only
B.1 and 3 only
C.2 and 3 only
D.1,2,3

我唔明點解係D = = ..我1同3都唔明 .. 佢冇講明個object距離塊鏡幾遠. .如果近既話唔係會放大架咩? 點解會係縮細,,3完全唔明佢up乜-.- " " convex mirror究竟咩黎. .thx~

作者: Royal 時間: 7/8/2009 07:43 PM
CE out-syl =) file可close

作者: 小霞的fans 時間: 8/8/2009 08:21 PM
另外仲有1題..

two connected boxes are stationary on a frictionless surface and Lily uses 50N to pull them to the right.the boxes move at the same acceleration and friction is megligible.

The string connecting the boxes breaks suddenly.Lily says that the second box would stop.comment on her second. 呢題唔識 - -"" THX~

口----口------50N
(向右行)
幅圖大約係咁

作者: 超夢夢的夢境 時間: 8/8/2009 09:02 PM

CE out-syl =) file可close
Royal 發表於 7/8/2009 07:43 PM

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抗議close file!
雖然直情係AL out-syl

convex mirror 同 concave lens 類似
不過光線全部o係同一面
concave mirror 就同 convex lens類似

另外仲有1題..

two connected boxes are stationary on a frictionless surface and Lily uses 50N to pull them to the right.the boxesmoveat the same acceleration and friction is megligible.

The str ...
小霞的fans 發表於 8/8/2009 08:21 PM

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comment on her statement吧

如果沒理解錯的話
incorrect
There will be no net force exerted on the second box after the string is broken.
By Newton's First Law of Motion, the second box would continue to move in a straight line with a constant speed rather than stop.

作者: 小霞的fans 時間: 9/8/2009 01:58 PM

抗議close file!
雖然直情係AL out-syl

convex mirror 同 concave lens 類似
不過光線全部o係同一面
concave mirror 就同 convex lens類似

comment on her statement吧
如果沒理解錯的話
...
超夢夢的夢境發表於 8/8/2009 01:02 AM

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冇net force既話唔係一係stop一係move with uniform speed..
點解唔係stop而係繼續行 ?

作者: sapphire 時間: 9/8/2009 02:34 PM
本帖最後由 sapphire 於 9/8/2009 02:43 PM 編輯

冇net force既話唔係一係stop一係move with uniform speed..
點解唔係stop而係繼續行 ?
小霞的fans 發表於 9/8/2009 01:58 PM

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可是那個box在繩斷之前一直在動啊

By Newton's 1st law, a body is either at rest or move in a straight line with constant velocity when there is no net force.
就是說如果沒有force act在某body上, 那body就是維持著之前的motion
如果之前是at rest的話就繼續at rest, 如果之前是在移動的話就以constant velocity繼續移動

繩斷之後, 地下沒有friction, 因此沒有任何force act在那個box上 (net force = 0), 那個box就維持著繩斷之前的motion, 以繩斷之前那一刻的velocity繼續同一方向移動

作者: Royal 時間: 9/8/2009 09:13 PM

冇net force既話唔係一係stop一係move with uniform speed..
點解唔係stop而係繼續行 ?
小霞的fans 發表於 9/8/2009 01:58 PM

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其實冇net force係會維持當時既velocity
如果當時velocity = 0, then佢既velocity之後都會係0
咁你一直有拉佢, 只係無啦啦斷左, 咁應該velocity > 0
所以應該係繼續郁緊=)

作者: 小霞的fans 時間: 19/8/2009 06:19 PM

其實冇net force係會維持當時既velocity
如果當時velocity = 0, then佢既velocity之後都會係0
咁你一直有拉佢, 只係無啦啦斷左, 咁應該velocity > 0
所以應該係繼續郁緊=)
Royal 發表於 9/8/2009 01:13 AM

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唔該哂2位><明白..
mgsinθ同mgcosθ係咩黎架><我唔記得左..
點解畫一個box slide down through a plane 既free body diagram果時,
唔使畫mgsinθ既箭咀既!?

作者: simon199392 時間: 19/8/2009 08:37 PM
mgsinθ係將個weight拆開左, 做左resolution得出黎

作者: 小霞的fans 時間: 27/8/2009 03:57 PM

mgsinθ係將個weight拆開左, 做左resolution得出黎
simon199392 發表於 19/8/2009 12:37 AM

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點解要將個weight 分解為mgsin同mgcosθ ??

作者: simon199392 時間: 28/8/2009 11:12 AM
因為weight同friction同normal reaction 既direction唔同,
分解左做mgsin同mgcosθ, d force既direction係一樣, 約(?)得走,

PS: mgcosθ=normal reaction

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