As oppositely moving pulses of the same shape (one upward, one downward) on a string pass through each other, at one particular instant the string shows no displacement from the equilibrium position at any point. What has happened to the energy carried by the pulses at this instant of time?

It is all kinetic energy.
It is all internal energy.
Each pulse separately has zero total energy.
It is momentum.

Question

As oppositely moving pulses of the same shape (one upward, one downward) on a string pass through each other, at one particular instant the string shows no displacement from the equilibrium position at any point. What has happened to the energy carried by the pulses at this instant of time?

It is all kinetic energy.     
 It is all internal energy. 
Each pulse separately has zero total energy. 
It is momentum.

anonymous · Answer

A simple thing to imagine but those answer options make it tough..
When the peak and trough align, you get perfect destructive interference at each point. The amplitudes of the displacemetnt cancel (they are in the opposite direction). The energy being carried by both is still there though.. perhaps it is momentum..?

anonymous · Answer

It's all kinetic, since there is no tension in the string, hence no potential energy.  The string is, of course, in motion, as you will observe a moment later, when both pulses re-emerge.

Momentum is separate from energy.