Equilibrium in SHM Question

[deleted388502]

At a particular time, the amplitude of String I is zero. What can be said about the energy of the standing wave at this point?

A. The energy of the wave is zero.
B. The wave has only kinetic energy.
C. The wave has only potential energy.
D. The wave has both potential energy and kinetic energy.

I'm so confused as to where 'equilibrium' is in SHM because the answer to this is B. A previous question asked where the string moves most, and it was at the point of amplitude, so I thought KEmax was at the point of amplitude.

This question confuses me because I'm assuming it's asking what energy this wave has when it's at zero, and I don't understand why that's max KE, because I thought max KE was when a wave was at its max displacement from 0, which was equilibrium point.

This is TBR Chapter 5, Passage II, Phase II.

Thanks!

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[t5Nitro]

As it oscillates, max KE is at zero amplitude and then max PE occurs at both crests and troughs. Somewhere in between those you will have both KE and PE. It's like a spring system where the equilibrium position is where the KE is maximized because the velocity is greatest. Like a spring system, at max displacement then you convert that into PE. Think of it like this and it should be easy to remember.

 

[deleted388502]

As it oscillates, max KE is at zero amplitude and then max PE occurs at both crests and troughs. Somewhere in between those you will have both KE and PE. It's like a spring system where the equilibrium position is where the KE is maximized because the velocity is greatest. Like a spring system, at max displacement then you convert that into PE. Think of it like this and it should be easy to remember.

literally best explanation ever! thanks for the comparison, this was a great help.