Speed of standing vs traveling waves

[ipodtouch]

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At a particular time, the amplitude of a standing string is zero. What can be said about the standing wave at this point?
A.) the wave E is zero
B.) the wave has only KE
C.) the wave has only PE
D.) the wave has both PE and KE

The answer is C

Isnt this wrong? the A=0 of a standing wave is at the node when string doesnt displace.
When A=max, string displaces the most and there should the greatest E at C.

Wtf??

 

[hellocubed]

Wow...

Bad question? (I say this for every goddamn BR question that i don't understand)



Wave velocity is supposed to be the same throughout the wave, so there shouldn't be any change in KE or PE.
😕

 

[chiddler]

Surely it must be referring to a non-node point on the wave.

But it raises an interesting question: what are the energetics like on nodes of a standing wave?

 

[UrshumMurshum]

My interpretation is that since it is a standing wave, the wave itself is not moving laterally only vertically up and down. However at a node the vertical velocities are canceled resulting in no net movement vertically either.

Since the point is not moving horizontally or vertically it must not have any kinetic energy which requires a non-zero velocity term.

Therefore it can only have potential energy.

 

[hellocubed]

At a particular time, the amplitude of a standing string is zero. What can be said about the standing wave at this point?
A.) the wave E is zero
B.) the wave has only KE
C.) the wave has only PE
D.) the wave has both PE and KE

The answer is C

Isnt this wrong? the A=0 of a standing wave is at the node when string doesnt displace.
When A=max, string displaces the most and there should the greatest E at C.

Wtf??

I remembered this question from BR and just looked this up. The answer is B.
Not C

Which is even more confusing because the string is not moving at all.


Why is there only in KE at A=0?
Any explanation would be great, considering there is no velocity.

 

[ipodtouch]

Oh Crap I meant B.

The answer to the question is "only has KE"

Why is this when the wave itself is not displaced at all at A=0?

 

[ipodtouch]

Is this problem talking about the displacement of the string? Or the horizontal progress of what is the "wave"??