TBR Physics Question Mistake???

[Mwebs]

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So this is a question from TBR chapter on waves:

If deep-water ocean waves elevate a stationary boat
every 4 seconds and the distance between every third
crest is 150 m, what is the average speed of the waves?
A. 0.08 m/s
B. 12.5 m/s
C. 37.5 m/s
D. 113 m/s

Sooooo I was able to get the right answer while doing the questions (B). However, this takes the wavelength to be 50m (150/3) I think they made a mistake with what "every third" means. Every third means that in those 150 m there are 3 crests, but only 2 wavelengths between them! Meaning from crest 1 to crest 2 is one wavelength and then from crest 2 to 3 is the second. I have no clue where their 3 wavelengths come from. So shouldn't the wavelength be 75???

 

[Romz]

So this is a question from TBR chapter on waves:

If deep-water ocean waves elevate a stationary boat
every 4 seconds and the distance between every third
crest is 150 m, what is the average speed of the waves?
A. 0.08 m/s
B. 12.5 m/s
C. 37.5 m/s
D. 113 m/s

Sooooo I was able to get the right answer while doing the questions (B). However, this takes the wavelength to be 50m (150/3) I think they made a mistake with what "every third" means. Every third means that in those 150 m there are 3 crests, but only 2 wavelengths between them! Meaning from crest 1 to crest 2 is one wavelength and then from crest 2 to 3 is the second. I have no clue where their 3 wavelengths come from. So shouldn't the wavelength be 75???

No i don't think so; I got what they meant.

Crest-----------Crest-----------Crest-----------Crest
--------lambda 1-----lambda 2------lambda 3

I get what you mean, but if we take the basal crest to be

Distance Between Crest 1 is 5o Total
Distance Between Crest 2 is 100 total
Distance between third crest is 150 total

By the way you said it, distance between first crest would be 0 and then we would get two crests of lambda = 75. Doesn't really make sense.

Hope this clears it up.


Edit: Thought about it more and if the question were:

blah blah blah distance between Crest Number 1 and Crest Number Three is 150

Then our lambda would be as you said; 75

 

[ilovemedi]

Sorry to bring this up, but if the "distance between every third crest is 150 m" and a wavelength is the distance between 2 crests, how would we figure out the wavelength. Intiially, i did 150/3 crests = 50meters for each crest... but then I multiplied 50*2 since 2 crests = 1 wavelength.... obviously thats wrong!

 

[ilovemedi]

Sorry to bring this up, but if the "distance between every third crest is 150 m" and a wavelength is the distance between 2 crests, how would we figure out the wavelength. Intiially, i did 150/3 crests = 50meters for each crest... but then I multiplied 50*2 since 2 crests = 1 wavelength.... obviously thats wrong!

edit: okay, now I get what everyone is saying, isn't the wavelength 75 between each crests? because there's 2 wavelengths between the 3 crests (as pictured above), thus 150/2 = 75...