The following applet shows suposition of two impulses.
[color=blue][b]BLUE[/b][/color] curve is the sum of two [b]BLACK[/b] impulses, [color=red][b]RED[/b][/color] curve is the velocity distribution Vy(x).
First, click the checkbox paused to make the simulation paused when two impulses are very close to each other.
Notice that when the sum of two impulses is maximum, the velocity curve is a horizontal line.
This means that all the energy goes to potential energy and kinetic energy is zero.
If you click + checkbox, one of the impulse will be up side down.
And the sum of two impulses becomes a horizontal line.
It appears that those two wave cencel [b][color=blue]displacement[/color][/b] completely, but check out the [b][color=red]velocity[/color][/b] distribution at that moment.
You can change the velocity and impulse width with slider,too.
2012/10/19 I have modified the code, so that user can drag the wave and change it's magnitude with mouse. Have fun and Try it! ;-)