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[Phy] Longitudinal Wave

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Longitudinal Wave

Answer: B

但particles A and I 唔係moving to the right嗎???
如果係咁ANS應該係D喎
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回覆 #1 vanessa_ky 的帖子

Particles會在crests/troughs果一刻momentarily at rest. 在圖中,A同I係MOMENTARILY AT REST (何況果圖都顯示左係-.-)
佢地都MOMENTARILY AT REST,又點會moving to the left呢

所以答案係B

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我覺得條題目係有D問題= =

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particles have zero displacement when they are at the centre of compression/rarefaction.
-> A and I are not momentarily at rest. they are moving!

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A and I is not momentarily at rest
they are compreesion /rarefaction

what is mean  at rest in longitudinal wave?
the particle is in Amphitide = at rest

you can draw the graph show that!

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引用:
原帖由 阿哈 於 2009-6-13 09:15 PM 發表
Particles會在crests/troughs果一刻momentarily at rest. 在圖中,A同I係MOMENTARILY AT REST (何況果圖都顯示左係-.-)
佢地都MOMENTARILY AT REST,又點會moving to the left呢

所以答案係B
問題係問incorrect 見到ans就自圓其說

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A to left
I to right
There is somethings wrong in the question

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回覆 #2 阿哈 的帖子

Why do you say A and I are in trough...they are in eq....... so that they hv highest KE

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Agree with the above. I think the question doesn't make sense. I hope it is not a past paper question!!!!

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nothing wrong in the question.

ANSWER: D


checked with professional

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回覆 #10 vanessa_ky 的帖子

Mmmmmmmmmmmm, that beats me. Do you mind offering an explanation?

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plz refer to the previous posts.

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A and I are inphase

I is moving towards left.

so A is moving toward left too,

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Longitudinal Wave


Displacement-distance graph


Note:
1. Right hand side is taken to be positive
2. The purple arrow shows the direction of propagation
3. The blue line is followed by the light blue line.



Statements Analysis
(1) The distance between particles E and M is equal to one wavelength. (Correct.)
(2) Particles A and I are momentarily at rest. (They are at equilibrium position with the highest speed.)
(3) Particles A and I are moving to the left. (They should be moving to the right.)

So, statements (2) and (3) are incorrect.




I think the answer should be D instead of B. =]
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There are no trough or crest in LW.
I also agree with ANS D as you said.

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