# Homework Help: Which diagram below best representsthe shape ofthe rope when both puls

1. Apr 22, 2013

### cmkc109

1. The problem statement, all variables and given/known data

The diagram shows two pulses, each of length , traveling toward each other at equal speed in a rope

Which diagram below best represent sthe shape ofthe rope when both pulses are in region AB?

2. Relevant equations

3. The attempt at a solution

The answer is the last option, it will be a flat line

but this looks like constructive to me, meaning they should add up since they are the same when approaching...

greatly appreciated if someone can explain with a diagram ,thanks

And same as #73, i should dont know how to picture how these things work ...

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Last edited: Apr 22, 2013
2. Apr 22, 2013

### CWatters

Initially the two +ve peaks collide and you do indeed have constructive interference and a +ve peak twice the height BUT when that happens the two waves only overlap by λ/2 and they aren't entirely within the region AB.

The +ve peaks continue past each other until the +ve peak of one overlaps with the negative peak of the other and you get destructive interference and a flat line. At this point both waves are within AB. So flat line is the answer.

If you let the clock run further the waves keep going until the -ve part of one overlaps with the -ve part of the other. You get constructive interference again only this time a -ve peak twice the height forms. Again this happens when they overlap by λ/2 and they aren't entirely within the region AB.

Last edited: Apr 22, 2013