Maike J.

asked • 01/19/15

wavelength of the disturbance

A set of circular ripples is produced on the surface of a pond by throwing a stone into water. At a certain instant, the first crest is 4 m from the point where the stone hit the water, and the fourth crest is 70cm from the same point. What is the wavelength of the disturbance?

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Jon P. answered • 01/20/15

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The distance between the 1st crest and the 4th is 70 cm - 4 cm = 66 cm.
 
So the length of each wave is 1/3 of that (since the measurements were taken 3 crests apart), which is 22 cm.
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Anton K.

It is not 4 centimeters it is actually in meters. The right answer should be 1.1m, which I got as a sum of distances   400cm + 70cm = 470cm divided by the overall 4 points. The result is 117.5cm which is 1.1m with 2 significant figures.
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01/21/15

Jon P.

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Yes, you are correct that I misread the question.  My apologies!
 
But that is still not the correct analysis.  At the moment they describe, the first crest has traveled 4 meters from the point where the stone hit the water, and the fourth crest has traveled 70 cm, or .7 meters.  The distance from the first to the fourth crest is 4 - .7 meters = 3.3 meters.  And it covers three wavelengths.  So the wavelength is exactly 1.1 meters.
 
 
 
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01/22/15

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